$ES
EVERSOURCE ENERGY Stock $es

$es Overview Financials Valuation SEC Filings Company Website

2013 Q4 Form 10-K Financial Statement

#000007274114000011 Filed on February 25, 2014

Income Statement

Concept	2013 Q4	2012 Q4	2012 Q1
Revenue	$1.778B	$1.684B	$1.100B
YoY Change	5.56%	57.68%	-10.99%
Cost Of Revenue
YoY Change
Gross Profit
YoY Change
Gross Profit Margin
Selling, General & Admin
YoY Change
% of Gross Profit
Research & Development
YoY Change
% of Gross Profit
Depreciation & Amortization	$147.2M	$149.2M	$104.6M
YoY Change	-1.34%	87.91%	-16.72%
% of Gross Profit
Operating Expenses	$1.417B	$1.353B	$885.2M
YoY Change	4.77%	53.15%	-12.17%
Operating Profit	$360.6M	$331.4M	$214.4M
YoY Change	8.81%	79.23%	-5.72%
Interest Expense	-$88.10M	-$84.10M	$66.45M
YoY Change	4.76%	28.01%	13.49%
% of Operating Profit	-24.43%	-25.38%	30.99%
Other Income/Expense, Net	$8.200M	$4.800M	$8.773M
YoY Change	70.83%	-44.19%	-14.93%
Pretax Income	$280.8M	$252.1M	$156.7M
YoY Change	11.38%	97.26%	-12.51%
Income Tax	$101.5M	$75.50M	$55.96M
% Of Pretax Income	36.15%	29.95%	35.71%
Net Earnings	$179.2M	$176.6M	$100.8M
YoY Change	1.47%	53.83%	-12.8%
Net Earnings / Revenue	10.08%	10.49%	9.17%
Basic Earnings Per Share
Diluted Earnings Per Share	$560.2K	$559.0K	$565.0K
COMMON SHARES
Basic Shares Outstanding	315.1M shares	313.9M shares	178.1M shares
Diluted Shares Outstanding			178.4M shares

Balance Sheet

Concept	2013 Q4	2012 Q4	2012 Q1
SHORT-TERM ASSETS
Cash & Short-Term Investments	$43.00M	$46.00M	$346.0M
YoY Change	-6.52%	-41.03%	264.21%
Cash & Equivalents	$43.00M	$46.00M	$283.0M
Short-Term Investments			$63.00M
Other Short-Term Assets	$214.3M	$199.9M	$94.74M
YoY Change	7.17%	77.52%	-80.39%
Inventory	$303.0M	$268.0M	$219.0M
Prepaid Expenses
Receivables	$765.0M	$792.8M	$485.8M
Other Receivables	$17.00M	$0.00	$0.00
Total Short-Term Assets	$2.087B	$2.227B	$1.523B
YoY Change	-6.3%	64.08%	8.28%
LONG-TERM ASSETS
Property, Plant & Equipment	$17.58B	$16.61B	$10.61B
YoY Change	5.85%	59.62%	9.23%
Goodwill	$3.519B	$3.519B	$287.6M
YoY Change	0.0%	1073.13%
Intangibles
YoY Change
Long-Term Investments	$489.0M	$400.0M	$74.00M
YoY Change	22.25%	18947.62%	39.62%
Other Assets	$291.5M	$327.8M	$171.6M
YoY Change	-11.05%	89.94%	-94.19%
Total Long-Term Assets	$8.132B	$9.471B	$3.842B
YoY Change	-14.13%	143.68%	-70.47%
TOTAL ASSETS
Total Short-Term Assets	$2.087B	$2.227B	$1.523B
Total Long-Term Assets	$8.132B	$9.471B	$3.842B
Total Assets	$27.80B	$28.30B	$15.98B
YoY Change	-1.79%	80.88%	10.82%
SHORT-TERM LIABILITIES
YoY Change
Accounts Payable	$742.3M	$764.4M	$412.9M
YoY Change	-2.89%	20.7%	-3.76%
Accrued Expenses
YoY Change
Deferred Revenue
YoY Change
Short-Term Debt	$1.093B	$1.120B	$660.0M
YoY Change	-2.41%	253.31%	249.21%
Long-Term Debt Due	$533.3M	$763.3M	$267.3M
YoY Change	-30.13%	130.21%	304.98%
Total Short-Term Liabilities	$3.276B	$3.644B	$1.968B
YoY Change	-10.1%	87.08%	63.02%
LONG-TERM LIABILITIES
Long-Term Debt	$7.777B	$7.200B	$4.977B
YoY Change	8.01%	56.02%	3.8%
Other Long-Term Liabilities	$923.1M	$967.6M	$414.0M
YoY Change	-4.6%	130.37%	-84.69%
Total Long-Term Liabilities	$6.976B	$7.984B	$4.751B
YoY Change	-12.63%	64.95%	-36.64%
TOTAL LIABILITIES
Total Short-Term Liabilities	$3.276B	$3.644B	$1.968B
Total Long-Term Liabilities	$6.976B	$7.984B	$4.751B
Total Liabilities	$10.25B	$11.63B	$6.719B
YoY Change	-11.84%	71.3%	-35.5%
SHAREHOLDERS EQUITY
Retained Earnings	$2.126B	$1.803B	$1.699B
YoY Change	17.93%	9.13%
Common Stock	$1.665B	$1.663B	$981.6M
YoY Change	0.17%	69.6%
Preferred Stock
YoY Change
Treasury Stock (at cost)	-$326.5M	-$338.6M	-$344.8M
YoY Change	-3.57%	-2.32%
Treasury Stock Shares	17.80M shares	18.46M shares	18.79M shares
Shareholders Equity	$9.612B	$9.237B	$4.068B
YoY Change
Total Liabilities & Shareholders Equity	$27.80B	$28.30B	$15.98B
YoY Change	-1.79%	80.88%	10.81%

Cashflow Statement

Concept	2013 Q4	2012 Q4	2012 Q1
OPERATING ACTIVITIES
Net Income	$179.2M	$176.6M	$100.8M
YoY Change	1.47%	53.83%	-12.8%
Depreciation, Depletion And Amortization	$147.2M	$149.2M	$104.6M
YoY Change	-1.34%	87.91%	-16.72%
Cash From Operating Activities	$486.5M	$365.2M	$8.816M
YoY Change	33.21%	345.37%	-97.63%
INVESTING ACTIVITIES
Capital Expenditures	-$383.0M	-$390.5M	$304.3M
YoY Change	-1.92%	19.2%	28.56%
Acquisitions
YoY Change
Other Investing Activities	$800.0K	-$16.10M	-$2.448M
YoY Change	-104.97%	-185.19%	646.34%
Cash From Investing Activities	-$382.2M	-$406.6M	-$302.5M
YoY Change	-6.0%	31.71%	27.65%
FINANCING ACTIVITIES
Cash Dividend Paid
YoY Change
Common Stock Issuance & Retirement, Net
YoY Change
Debt Paid & Issued, Net
YoY Change
Cash From Financing Activities	-118.9M	13.70M	$570.5M
YoY Change	-967.88%	-93.68%	-496.56%
NET CHANGE
Cash From Operating Activities	486.5M	365.2M	$8.816M
Cash From Investing Activities	-382.2M	-406.6M	-$302.5M
Cash From Financing Activities	-118.9M	13.70M	$570.5M
Net Change In Cash	-14.60M	-27.70M	$276.8M
YoY Change	-47.29%	177.0%	-3544.75%
FREE CASH FLOW
Cash From Operating Activities	$486.5M	$365.2M	$8.816M
Capital Expenditures	-$383.0M	-$390.5M	$304.3M
Free Cash Flow	$869.5M	$755.7M	-$295.5M
YoY Change	15.06%	84.5%	-317.14%

Facts In Submission

Frame	Concept Type	Concept / XBRL Key	Value	Unit
CY2012Q4	us-gaap	Cash Cash	45748000	USD
CY2012Q4	us-gaap	Energy Related Inventory EnergyRelatedInventory	267713000	USD
CY2012Q4	us-gaap	Assets Current AssetsCurrent	2227295000	USD
CY2013Q4	us-gaap	Regulatory Assets Noncurrent RegulatoryAssetsNoncurrent	3758694000	USD
CY2013	us-gaap	Depreciation Depreciation	610777000	USD
CY2012	us-gaap	Other Comprehensive Income Loss Available For Sale Securities Adjustment Net Of Tax OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax	217000	USD
CY2013	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	25714000	USD
CY2012	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	-4356000	USD
CY2013	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	26823000	USD
CY2012	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	-2168000	USD
CY2013	us-gaap	Other Comprehensive Income Loss Derivatives Qualifying As Hedges Net Of Tax OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesNetOfTax	2049000	USD
CY2013	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	-224700000	USD
CY2013	us-gaap	Other Comprehensive Income Loss Available For Sale Securities Adjustment Net Of Tax OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax	-940000	USD
CY2013	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	7682000	USD
CY2013	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	812830000	USD
CY2013Q4	us-gaap	Regulatory Liability Current RegulatoryLiabilityCurrent	204278000	USD
CY2012Q4	us-gaap	Regulatory Liability Current RegulatoryLiabilityCurrent	134115000	USD
CY2011	us-gaap	Operating Income Loss OperatingIncomeLoss	794176000	USD
CY2011	us-gaap	Interest Expense Long Term Debt InterestExpenseLongTermDebt	231630000	USD
CY2011	us-gaap	Cost Of Purchased Power CostOfPurchasedPower	1657914000	USD
CY2012	us-gaap	Depreciation Depreciation	519010000	USD
CY2012	us-gaap	Utilities Operating Expense Maintenance And Operations UtilitiesOperatingExpenseMaintenanceAndOperations	1583070000	USD
CY2011	us-gaap	Nonoperating Income Expense NonoperatingIncomeExpense	27715000	USD
CY2012	us-gaap	Nonoperating Income Expense NonoperatingIncomeExpense	19742000	USD
CY2013Q4	us-gaap	Accounts Payable Current AccountsPayableCurrent	742251000	USD
CY2012Q4	us-gaap	Accounts Payable Current AccountsPayableCurrent	764350000	USD
CY2013Q4	us-gaap	Notes Payable To Bank Current NotesPayableToBankCurrent	1093000000	USD
CY2012Q4	us-gaap	Notes Payable To Bank Current NotesPayableToBankCurrent	1120196000	USD
CY2013Q4	us-gaap	Long Term Debt Current LongTermDebtCurrent	533346000	USD
CY2012Q4	us-gaap	Long Term Debt Current LongTermDebtCurrent	763338000	USD
CY2013Q4	us-gaap	Regulatory Liability Noncurrent RegulatoryLiabilityNoncurrent	502984000	USD
CY2012Q4	us-gaap	Derivative Liabilities Noncurrent DerivativeLiabilitiesNoncurrent	882654000	USD
CY2013Q4	us-gaap	Pension And Other Postretirement Defined Benefit Plans Liabilities Noncurrent PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent	896844000	USD
CY2012Q4	us-gaap	Pension And Other Postretirement Defined Benefit Plans Liabilities Noncurrent PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent	2130497000	USD
CY2013Q4	us-gaap	Other Liabilities Noncurrent OtherLiabilitiesNoncurrent	923053000	USD
CY2012Q4	us-gaap	Other Liabilities Noncurrent OtherLiabilitiesNoncurrent	967561000	USD
CY2013Q4	us-gaap	Liabilities Noncurrent LiabilitiesNoncurrent	6975957000	USD
CY2012Q4	us-gaap	Liabilities Noncurrent LiabilitiesNoncurrent	7984221000	USD
CY2013Q4	us-gaap	Long Term Debt Noncurrent LongTermDebtNoncurrent	7776833000	USD
CY2012Q4	us-gaap	Long Term Debt Noncurrent LongTermDebtNoncurrent	7200156000	USD
CY2013Q4	us-gaap	Temporary Equity Carrying Amount Attributable To Noncontrolling Interest TemporaryEquityCarryingAmountAttributableToNoncontrollingInterest	155568000	USD
CY2012Q4	us-gaap	Temporary Equity Carrying Amount Attributable To Noncontrolling Interest TemporaryEquityCarryingAmountAttributableToNoncontrollingInterest	155568000	USD
CY2013Q4	us-gaap	Common Stock Value CommonStockValue	1665351000	USD
CY2012Q4	us-gaap	Common Stock Value CommonStockValue	1662547000	USD
CY2013Q4	us-gaap	Additional Paid In Capital AdditionalPaidInCapital	6192765000	USD
CY2012Q4	us-gaap	Retained Earnings Accumulated Deficit RetainedEarningsAccumulatedDeficit	1802714000	USD
CY2013Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	46031000	USD
CY2012Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	72854000	USD
CY2013Q4	us-gaap	Treasury Stock Value TreasuryStockValue	-326537000	USD
CY2012Q4	us-gaap	Treasury Stock Value TreasuryStockValue	-338624000	USD
CY2013Q4	us-gaap	Stockholders Equity StockholdersEquity	9611528000	USD
CY2012Q4	us-gaap	Stockholders Equity StockholdersEquity	9237050000	USD
CY2013Q4	us-gaap	Capitalization Longterm Debt And Equity CapitalizationLongtermDebtAndEquity	17543929000	USD
CY2012Q4	us-gaap	Capitalization Longterm Debt And Equity CapitalizationLongtermDebtAndEquity	16592774000	USD
CY2013Q4	us-gaap	Liabilities And Stockholders Equity LiabilitiesAndStockholdersEquity	27795537000	USD
CY2012Q4	us-gaap	Liabilities And Stockholders Equity LiabilitiesAndStockholdersEquity	28302824000	USD
CY2012Q4	us-gaap	Regulatory Liability Noncurrent RegulatoryLiabilityNoncurrent	540162000	USD
CY2013Q4	us-gaap	Deferred Tax Liabilities Noncurrent DeferredTaxLiabilitiesNoncurrent	4029026000	USD
CY2012Q4	us-gaap	Deferred Tax Liabilities Noncurrent DeferredTaxLiabilitiesNoncurrent	3463347000	USD
CY2013Q4	us-gaap	Derivative Liabilities Noncurrent DerivativeLiabilitiesNoncurrent	624050000	USD
CY2012Q4	us-gaap	Additional Paid In Capital AdditionalPaidInCapital	6183267000	USD
CY2013Q4	us-gaap	Retained Earnings Accumulated Deficit RetainedEarningsAccumulatedDeficit	2125980000	USD
CY2012	us-gaap	Interest Expense InterestExpense	329945000	USD
CY2013	us-gaap	Revenues Revenues	7301204000	USD
CY2013	us-gaap	Income Loss From Continuing Operations Before Income Taxes Domestic IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic	1220630000	USD
CY2013Q4	us-gaap	Other Liabilities Current OtherLiabilitiesCurrent	702776000	USD
CY2012Q4	us-gaap	Other Liabilities Current OtherLiabilitiesCurrent	861691000	USD
CY2013Q4	us-gaap	Liabilities Current LiabilitiesCurrent	3275651000	USD
CY2012Q4	us-gaap	Liabilities Current LiabilitiesCurrent	3643690000	USD
CY2011	us-gaap	Revenues Revenues	4465657000	USD
CY2013	us-gaap	Cost Of Purchased Power CostOfPurchasedPower	2482954000	USD
CY2013	us-gaap	Interest Expense Other InterestExpenseOther	-2693000	USD
CY2012Q4	us-gaap	Goodwill Goodwill	3519401000	USD
CY2013Q4	us-gaap	Secured Long Term Debt SecuredLongTermDebt	0	USD
CY2012Q4	us-gaap	Secured Long Term Debt SecuredLongTermDebt	82139000	USD
CY2011	us-gaap	Amortization Of Regulatory Asset AmortizationOfRegulatoryAsset	91080000	USD
CY2013Q4	us-gaap	Goodwill Goodwill	3519401000	USD
CY2011	us-gaap	Depreciation Depreciation	302192000	USD
CY2012	us-gaap	Cost Of Purchased Power CostOfPurchasedPower	2084364000	USD
CY2012	us-gaap	Revenues Revenues	6273787000	USD
CY2012	us-gaap	Other Depreciation And Amortization OtherDepreciationAndAmortization	142019000	USD
CY2013Q4	us-gaap	Derivative Assets Noncurrent DerivativeAssetsNoncurrent	74155000	USD
CY2012Q4	us-gaap	Derivative Assets Noncurrent DerivativeAssetsNoncurrent	90612000	USD
CY2013Q4	us-gaap	Other Assets Noncurrent OtherAssetsNoncurrent	291537000	USD
CY2012Q4	us-gaap	Other Assets Noncurrent OtherAssetsNoncurrent	327766000	USD
CY2013Q4	us-gaap	Assets Noncurrent AssetsNoncurrent	8132302000	USD
CY2012Q4	us-gaap	Assets Noncurrent AssetsNoncurrent	9470519000	USD
CY2013Q4	us-gaap	Assets Assets	27795537000	USD
CY2012Q4	us-gaap	Assets Assets	28302824000	USD
CY2013Q4	us-gaap	Regulatory Assets Current RegulatoryAssetsCurrent	535791000	USD
CY2012Q4	us-gaap	Regulatory Assets Current RegulatoryAssetsCurrent	705025000	USD
CY2013Q4	us-gaap	Public Utilities Property Plant And Equipment Net PublicUtilitiesPropertyPlantAndEquipmentNet	17576186000	USD
CY2012Q4	us-gaap	Public Utilities Property Plant And Equipment Net PublicUtilitiesPropertyPlantAndEquipmentNet	16605010000	USD
CY2012	us-gaap	Taxes Excluding Income And Excise Taxes TaxesExcludingIncomeAndExciseTaxes	434207000	USD
CY2012	us-gaap	Operating Expenses OperatingExpenses	5155581000	USD
CY2013	us-gaap	Amortization Of Regulatory Asset AmortizationOfRegulatoryAsset	206322000	USD
CY2013	us-gaap	Taxes Excluding Income And Excise Taxes TaxesExcludingIncomeAndExciseTaxes	512230000	USD
CY2013	us-gaap	Operating Expenses OperatingExpenses	5771769000	USD
CY2012Q4	us-gaap	Marketable Securities Noncurrent MarketableSecuritiesNoncurrent	400329000	USD
CY2013	us-gaap	Operating Income Loss OperatingIncomeLoss	1529435000	USD
CY2012	us-gaap	Amortization Of Regulatory Asset AmortizationOfRegulatoryAsset	79762000	USD
CY2013	us-gaap	Other Depreciation And Amortization OtherDepreciationAndAmortization	42581000	USD
CY2011	us-gaap	Other Depreciation And Amortization OtherDepreciationAndAmortization	69912000	USD
CY2011	us-gaap	Taxes Excluding Income And Excise Taxes TaxesExcludingIncomeAndExciseTaxes	323610000	USD
CY2011	us-gaap	Operating Expenses OperatingExpenses	3671481000	USD
CY2011	nu	Energy Efficiency Programs EnergyEfficiencyPrograms	131415000	USD
CY2012	us-gaap	Operating Income Loss OperatingIncomeLoss	1118206000	USD
CY2011	us-gaap	Income Loss From Continuing Operations Before Income Taxes Domestic IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic	571466000	USD
CY2013	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	426941000	USD
CY2012	us-gaap	Interest Expense Long Term Debt InterestExpenseLongTermDebt	316987000	USD
CY2012	us-gaap	Interest Expense Other Long Term Debt InterestExpenseOtherLongTermDebt	6168000	USD
CY2011	us-gaap	Interest Expense Other Long Term Debt InterestExpenseOtherLongTermDebt	8611000	USD
CY2012	us-gaap	Interest Expense Other InterestExpenseOther	6790000	USD
CY2011	us-gaap	Interest Expense Other InterestExpenseOther	10184000	USD
CY2013	us-gaap	Interest Expense InterestExpense	338699000	USD
CY2011	us-gaap	Interest Expense InterestExpense	250425000	USD
CY2012	us-gaap	Income Loss From Continuing Operations Before Income Taxes Domestic IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic	808003000	USD
CY2012	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	274926000	USD
CY2011	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	170953000	USD
CY2013	us-gaap	Net Income Loss NetIncomeLoss	793689000	USD
CY2012	us-gaap	Net Income Loss NetIncomeLoss	533077000	USD
CY2011	us-gaap	Net Income Loss NetIncomeLoss	400513000	USD
CY2013	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	7682000	USD
CY2012	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	7132000	USD
CY2011	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	5820000	USD
CY2013	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	786007000	USD
CY2012	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	525945000	USD
CY2011	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	394693000	USD
CY2013	us-gaap	Utilities Operating Expense Maintenance And Operations UtilitiesOperatingExpenseMaintenanceAndOperations	1514986000	USD
CY2011	us-gaap	Utilities Operating Expense Maintenance And Operations UtilitiesOperatingExpenseMaintenanceAndOperations	1095358000	USD
CY2013	nu	Energy Efficiency Programs EnergyEfficiencyPrograms	401919000	USD
CY2012	nu	Energy Efficiency Programs EnergyEfficiencyPrograms	313149000	USD
CY2013	us-gaap	Nonoperating Income Expense NonoperatingIncomeExpense	29894000	USD
CY2012	us-gaap	Other Comprehensive Income Loss Derivatives Qualifying As Hedges Net Of Tax OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesNetOfTax	1971000	USD
CY2011	us-gaap	Other Comprehensive Income Loss Available For Sale Securities Adjustment Net Of Tax OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax	506000	USD
CY2011	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	-13645000	USD
CY2012	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	523777000	USD
CY2012	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	7132000	USD
CY2011	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	-27316000	USD
CY2011	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	5820000	USD
CY2011	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	367377000	USD
CY2011	us-gaap	Other Comprehensive Income Loss Derivatives Qualifying As Hedges Net Of Tax OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesNetOfTax	-14177000	USD
CY2012	nu	Sharesissuedvalueinconectionwithnstarmerger Sharesissuedvalueinconectionwithnstarmerger	680243000	USD
CY2012	nu	Sharesissuedinconnectionwithnstarmerger Sharesissuedinconnectionwithnstarmerger	136048595	shares
CY2013	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	431413000	USD
CY2013	us-gaap	Pension And Other Postretirement Benefit Expense PensionAndOtherPostretirementBenefitExpense	195698000	USD
CY2013	us-gaap	Increase Decrease In Regulatory Assets And Liabilities IncreaseDecreaseInRegulatoryAssetsAndLiabilities	24276000	USD
CY2013	us-gaap	Other Noncash Income Expense OtherNoncashIncomeExpense	56071000	USD
CY2013	us-gaap	Increase Decrease In Receivables IncreaseDecreaseInReceivables	163549000	USD
CY2013	us-gaap	Increase Decrease In Inventories IncreaseDecreaseInInventories	14811000	USD
CY2013	us-gaap	Increase Decrease In Income Taxes Receivable IncreaseDecreaseInIncomeTaxesReceivable	50950000	USD
CY2013	us-gaap	Increase Decrease In Accounts Payable IncreaseDecreaseInAccountsPayable	-54619000	USD
CY2013	us-gaap	Interest Expense Long Term Debt InterestExpenseLongTermDebt	340970000	USD
CY2013	us-gaap	Interest Expense Other Long Term Debt InterestExpenseOtherLongTermDebt	422000	USD
CY2013	us-gaap	Increase Decrease In Other Operating Capital Net IncreaseDecreaseInOtherOperatingCapitalNet	22623000	USD
CY2013	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	1663539000	USD
CY2013	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	1456787000	USD
CY2013	us-gaap	Proceeds From Sale And Maturity Of Marketable Securities ProceedsFromSaleAndMaturityOfMarketableSecurities	627532000	USD
CY2013	us-gaap	Payments To Acquire Marketable Securities PaymentsToAcquireMarketableSecurities	679784000	USD
CY2013	us-gaap	Payments For Proceeds From Other Investing Activities PaymentsForProceedsFromOtherInvestingActivities	-67816000	USD
CY2013	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-1441223000	USD
CY2013	us-gaap	Repayments Of Secured Debt RepaymentsOfSecuredDebt	82139000	USD
CY2013	us-gaap	Repayments Of Long Term Debt RepaymentsOfLongTermDebt	929885000	USD
CY2011	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	196761000	USD
CY2011	us-gaap	Pension And Other Postretirement Benefit Expense PensionAndOtherPostretirementBenefitExpense	133000000	USD
CY2011	us-gaap	Increase Decrease In Regulatory Assets And Liabilities IncreaseDecreaseInRegulatoryAssetsAndLiabilities	70863000	USD
CY2011	us-gaap	Other Noncash Income Expense OtherNoncashIncomeExpense	-48772000	USD
CY2011	us-gaap	Increase Decrease In Receivables IncreaseDecreaseInReceivables	-17570000	USD
CY2011	us-gaap	Increase Decrease In Inventories IncreaseDecreaseInInventories	11033000	USD
CY2011	us-gaap	Increase Decrease In Income Taxes Receivable IncreaseDecreaseInIncomeTaxesReceivable	-49642000	USD
CY2011	us-gaap	Increase Decrease In Accounts Payable IncreaseDecreaseInAccountsPayable	18916000	USD
CY2011	us-gaap	Increase Decrease In Other Operating Capital Net IncreaseDecreaseInOtherOperatingCapitalNet	-12569000	USD
CY2011	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	970386000	USD
CY2011	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	1076730000	USD
CY2011	us-gaap	Proceeds From Sale And Maturity Of Marketable Securities ProceedsFromSaleAndMaturityOfMarketableSecurities	149441000	USD
CY2011	us-gaap	Payments To Acquire Marketable Securities PaymentsToAcquireMarketableSecurities	151972000	USD
CY2011	us-gaap	Payments For Proceeds From Other Investing Activities PaymentsForProceedsFromOtherInvestingActivities	-60674000	USD
CY2011	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-1018587000	USD
CY2011	us-gaap	Repayments Of Secured Debt RepaymentsOfSecuredDebt	69312000	USD
CY2011	us-gaap	Repayments Of Long Term Debt RepaymentsOfLongTermDebt	369586000	USD
CY2011	us-gaap	Proceeds From Payments For Other Financing Activities ProceedsFromPaymentsForOtherFinancingActivities	-7123000	USD
CY2011	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	31365000	USD
CY2011	us-gaap	Cash And Cash Equivalents Period Increase Decrease CashAndCashEquivalentsPeriodIncreaseDecrease	-16836000	USD
CY2010Q4	us-gaap	Cash Cash	23395000	USD
CY2013	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	462741000	USD
CY2013	us-gaap	Payments Of Dividends Preferred Stock And Preference Stock PaymentsOfDividendsPreferredStockAndPreferenceStock	7682000	USD
CY2013	us-gaap	Proceeds From Repayments Of Short Term Debt ProceedsFromRepaymentsOfShortTermDebt	-397000000	USD
CY2013	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	1680000000	USD
CY2011	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	194555000	USD
CY2011	us-gaap	Payments Of Dividends Preferred Stock And Preference Stock PaymentsOfDividendsPreferredStockAndPreferenceStock	5559000	USD
CY2011	us-gaap	Proceeds From Repayments Of Short Term Debt ProceedsFromRepaymentsOfShortTermDebt	50000000	USD
CY2011	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	627500000	USD
CY2013	us-gaap	Pension And Other Postretirement Benefit Contributions PensionAndOtherPostretirementBenefitContributions	342184000	USD
CY2011	us-gaap	Pension And Other Postretirement Benefit Contributions PensionAndOtherPostretirementBenefitContributions	191101000	USD
CY2012	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	292000000	USD
CY2012	us-gaap	Pension And Other Postretirement Benefit Expense PensionAndOtherPostretirementBenefitExpense	218540000	USD
CY2012	us-gaap	Pension And Other Postretirement Benefit Contributions PensionAndOtherPostretirementBenefitContributions	295028000	USD
CY2012	us-gaap	Increase Decrease In Regulatory Assets And Liabilities IncreaseDecreaseInRegulatoryAssetsAndLiabilities	259853000	USD
CY2012	us-gaap	Other Noncash Income Expense OtherNoncashIncomeExpense	42852000	USD
CY2012	us-gaap	Increase Decrease In Receivables IncreaseDecreaseInReceivables	20214000	USD
CY2012	us-gaap	Increase Decrease In Inventories IncreaseDecreaseInInventories	-34321000	USD
CY2012	us-gaap	Increase Decrease In Income Taxes Receivable IncreaseDecreaseInIncomeTaxesReceivable	5450000	USD
CY2012	us-gaap	Increase Decrease In Accounts Payable IncreaseDecreaseInAccountsPayable	-128339000	USD
CY2012	us-gaap	Increase Decrease In Other Operating Capital Net IncreaseDecreaseInOtherOperatingCapitalNet	-8532000	USD
CY2012	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	1161229000	USD
CY2012	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	1472272000	USD
CY2012	us-gaap	Payments For Proceeds From Other Investing Activities PaymentsForProceedsFromOtherInvestingActivities	-35683000	USD
CY2012	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-1467924000	USD
CY2012	us-gaap	Proceeds From Sale And Maturity Of Marketable Securities ProceedsFromSaleAndMaturityOfMarketableSecurities	317294000	USD
CY2012	us-gaap	Payments To Acquire Marketable Securities PaymentsToAcquireMarketableSecurities	348629000	USD
CY2012	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	375047000	USD
CY2012	us-gaap	Payments Of Dividends Preferred Stock And Preference Stock PaymentsOfDividendsPreferredStockAndPreferenceStock	7029000	USD
CY2012	us-gaap	Proceeds From Repayments Of Short Term Debt ProceedsFromRepaymentsOfShortTermDebt	825000000	USD
CY2012	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	850000000	USD
CY2012	us-gaap	Repayments Of Long Term Debt RepaymentsOfLongTermDebt	839136000	USD
CY2012	us-gaap	Repayments Of Secured Debt RepaymentsOfSecuredDebt	114433000	USD
CY2012	us-gaap	Proceeds From Payments For Other Financing Activities ProceedsFromPaymentsForOtherFinancingActivities	6529000	USD
CY2012	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	345884000	USD
CY2012	us-gaap	Cash And Cash Equivalents Period Increase Decrease CashAndCashEquivalentsPeriodIncreaseDecrease	39189000	USD
CY2011Q4	us-gaap	Cash Cash	6559000	USD
CY2012Q4	us-gaap	Allowance For Doubtful Accounts Receivable Current AllowanceForDoubtfulAccountsReceivableCurrent	165500000	USD
CY2013Q4	us-gaap	Allowance For Doubtful Accounts Receivable Current AllowanceForDoubtfulAccountsReceivableCurrent	171300000	USD
CY2013Q4	us-gaap	Restricted Cash And Cash Equivalents RestrictedCashAndCashEquivalents	1700000	USD
CY2012Q4	us-gaap	Restricted Cash And Cash Equivalents RestrictedCashAndCashEquivalents	3300000	USD
CY2013Q4	nu	Cash Collateral Deposited CashCollateralDeposited	17900000	USD
CY2012Q4	nu	Cash Collateral Deposited CashCollateralDeposited	14600000	USD
CY2012Q4	nu	Rate Reduction Bond Deposits RateReductionBondDeposits	69400000	USD
CY2013	nu	Fuel Power Costs FuelPowerCosts	466500000	USD
CY2012	nu	Fuel Power Costs FuelPowerCosts	346800000	USD
CY2011	nu	Fuel Power Costs FuelPowerCosts	307900000	USD
CY2013	us-gaap	Public Utilities Allowance For Funds Used During Construction Capitalized Interest PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedInterest	-4100000	USD
CY2013	us-gaap	Public Utilities Allowance For Funds Used During Construction Capitalized Cost Of Equity PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity	7100000	USD
CY2013	nu	Public Utilities Allowance For Funds Used During Construction Capitalized Total PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedTotal	11200000	USD
CY2012	us-gaap	Public Utilities Allowance For Funds Used During Construction Capitalized Interest PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedInterest	-5300000	USD
CY2012	us-gaap	Public Utilities Allowance For Funds Used During Construction Capitalized Cost Of Equity PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity	6800000	USD
CY2012	nu	Public Utilities Allowance For Funds Used During Construction Capitalized Total PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedTotal	12100000	USD
CY2011	us-gaap	Public Utilities Allowance For Funds Used During Construction Capitalized Interest PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedInterest	-11800000	USD
CY2011	us-gaap	Public Utilities Allowance For Funds Used During Construction Capitalized Cost Of Equity PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity	22500000	USD
CY2011	nu	Public Utilities Allowance For Funds Used During Construction Capitalized Total PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedTotal	34300000	USD
CY2013	us-gaap	Public Utilities Allowance For Funds Used During Construction Rate PublicUtilitiesAllowanceForFundsUsedDuringConstructionRate	0.027	pure
CY2012	us-gaap	Public Utilities Allowance For Funds Used During Construction Rate PublicUtilitiesAllowanceForFundsUsedDuringConstructionRate	0.037	pure
CY2011	us-gaap	Public Utilities Allowance For Funds Used During Construction Rate PublicUtilitiesAllowanceForFundsUsedDuringConstructionRate	0.073	pure
CY2013	us-gaap	Excise And Sales Taxes ExciseAndSalesTaxes	144100000	USD
CY2012	us-gaap	Excise And Sales Taxes ExciseAndSalesTaxes	135000000	USD
CY2011	us-gaap	Excise And Sales Taxes ExciseAndSalesTaxes	137800000	USD
CY2013	us-gaap	Capital Expenditures Incurred But Not Yet Paid CapitalExpendituresIncurredButNotYetPaid	193100000	USD
CY2012	us-gaap	Capital Expenditures Incurred But Not Yet Paid CapitalExpendituresIncurredButNotYetPaid	160600000	USD
CY2011	us-gaap	Capital Expenditures Incurred But Not Yet Paid CapitalExpendituresIncurredButNotYetPaid	168500000	USD
CY2013	us-gaap	Interest Paid Net InterestPaidNet	343300000	USD
CY2012	us-gaap	Interest Paid Net InterestPaidNet	356500000	USD
CY2011	us-gaap	Interest Paid Net InterestPaidNet	256300000	USD
CY2011	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	-76600000	USD
CY2012	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	-12800000	USD
CY2013	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	50000000	USD
CY2013	us-gaap	Description Of Postemployment Benefits DescriptionOfPostemploymentBenefits	During 2013, NU recorded severance benefit expenses of $9.7 million in connection with the partial outsourcing of information technology functions made as part of ongoing post-merger integration. As of December 31, 2013, the severance accrual totaled $14.7 million and was included in Other Current Liabilities on the balance sheet.
CY2013	us-gaap	Postemployment Benefits Period Expense PostemploymentBenefitsPeriodExpense	9700000	USD
CY2013Q4	us-gaap	Postemployment Benefits Liability Current PostemploymentBenefitsLiabilityCurrent	14700000	USD
CY2012Q2	nu	Exchange Ratio ExchangeRatio	1.312	pure
CY2012Q2	nu	Number Of Nstar Shares Outstanding NumberOfNstarSharesOutstanding	103696000	shares
CY2013	us-gaap	Public Utilities Property Plant And Equipment Disclosure Of Composite Depreciation Rate For Plants In Service PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService	0.028	pure
CY2012Q2	us-gaap	Business Acquisition Equity Interests Issued Or Issuable Number Of Shares Issued BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued	136049000	shares
CY2012Q2	us-gaap	Business Acquisition Share Price BusinessAcquisitionSharePrice	36.79
CY2012Q2	us-gaap	Business Combination Consideration Transferred Other1 BusinessCombinationConsiderationTransferredOther1	33000000	USD
CY2012Q2	us-gaap	Business Combination Consideration Transferred1 BusinessCombinationConsiderationTransferred1	5038000000	USD
CY2012Q2	us-gaap	Business Acquisition Percentage Of Voting Interests Acquired BusinessAcquisitionPercentageOfVotingInterestsAcquired	1.00	pure
CY2012Q2	nu	Business Acquisition Number Of Shares Awarded Vested Immediately Prior To Merger BusinessAcquisitionNumberOfSharesAwardedVestedImmediatelyPriorToMerger	109000	shares
CY2012Q2	us-gaap	Business Combination Consideration Transferred Equity Interests Issued And Issuable BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable	5005000000	USD
CY2012Q4	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Property Plant And Equipment BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment	5155000000	USD
CY2012Q4	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Assets BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentAssets	2103000000	USD
CY2012Q4	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Current Liabilities BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities	1330000000	USD
CY2012Q4	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Liabilities Other BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther	2723000000	USD
CY2012Q4	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Liabilities Long Term Debt BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLongTermDebt	2099000000	USD
CY2012Q4	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Current Assets BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssets	739000000	USD
CY2012	us-gaap	Goodwill Acquired During Period GoodwillAcquiredDuringPeriod	3232000000	USD
CY2012Q4	us-gaap	Business Combination Acquisition Of Less Than100 Percent Noncontrolling Interest Fair Value BusinessCombinationAcquisitionOfLessThan100PercentNoncontrollingInterestFairValue	39000000	USD
CY2012Q4	us-gaap	Business Combination Recognized Identifiable Assets Acquired Goodwill And Liabilities Assumed Less Noncontrolling Interest BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedLessNoncontrollingInterest	5038000000	USD
CY2012	us-gaap	Business Acquisitions Pro Forma Revenue BusinessAcquisitionsProFormaRevenue	7004000000	USD
CY2011	us-gaap	Business Acquisitions Pro Forma Revenue BusinessAcquisitionsProFormaRevenue	7361000000	USD
CY2012	us-gaap	Business Acquisitions Pro Forma Net Income Loss BusinessAcquisitionsProFormaNetIncomeLoss	630000000	USD
CY2011	us-gaap	Business Acquisitions Pro Forma Net Income Loss BusinessAcquisitionsProFormaNetIncomeLoss	689000000	USD
CY2012	us-gaap	Business Acquisition Pro Forma Earnings Per Share Basic BusinessAcquisitionProFormaEarningsPerShareBasic	2.00
CY2012	us-gaap	Business Acquisition Pro Forma Earnings Per Share Diluted BusinessAcquisitionProFormaEarningsPerShareDiluted	1.99
CY2011	us-gaap	Business Acquisition Pro Forma Earnings Per Share Diluted BusinessAcquisitionProFormaEarningsPerShareDiluted	2.19
CY2011	us-gaap	Business Acquisition Pro Forma Earnings Per Share Basic BusinessAcquisitionProFormaEarningsPerShareBasic	2.20
CY2012	nu	Business Combination After Tax Transaction Costs BusinessCombinationAfterTaxTransactionCosts	32000000	USD
CY2011	nu	Business Combination After Tax Transaction Costs BusinessCombinationAfterTaxTransactionCosts	19000000	USD
CY2012	nu	After Tax Settlement Costs Incurred AfterTaxSettlementCostsIncurred	60000000	USD
CY2011	nu	After Tax Settlement Costs Incurred AfterTaxSettlementCostsIncurred	0	USD
CY2012	nu	After Tax Costs Transaction And Other Non Recurring Costs Excluded From Pro Forma Net Income AfterTaxCostsTransactionAndOtherNonRecurringCostsExcludedFromProFormaNetIncome	92000000	USD
CY2011	nu	After Tax Costs Transaction And Other Non Recurring Costs Excluded From Pro Forma Net Income AfterTaxCostsTransactionAndOtherNonRecurringCostsExcludedFromProFormaNetIncome	19000000	USD
CY2012	nu	Business Acquisition Description Of Settlement Agreements BusinessAcquisitionDescriptionOfSettlementAgreements	Regulatory Approvals: On February 15, 2012, NU and NSTAR reached comprehensive merger settlement agreements with the Massachusetts Attorney General and the DOER. The Attorney General settlement agreement covered a variety of rate-making and rate design issues, including a base distribution rate freeze through 2015 for NSTAR Electric, NSTAR Gas and WMECO and $15 million, $3 million and $3 million in the form of rate credits to their respective customers. The settlement agreement reached with the DOER covered the same rate-making and rate design issues as the Attorney General's settlement agreement, as well as a variety of matters impacting the advancement of Massachusetts clean energy policy established by the Green Communities Act and Global Warming Solutions Act. On April 4, 2012, the DPU approved the settlement agreements and the merger of NU and NSTAR. On March 13, 2012, NU and NSTAR reached a comprehensive merger settlement agreement with both the Connecticut Attorney General and the Connecticut Office of Consumer Counsel. The settlement agreement covered a variety of matters, including a $25 million rate credit to CL&P customers, a CL&P base distribution rate freeze until December 1, 2014, and the establishment of a $15 million fund for energy efficiency and other initiatives to be disbursed at the direction of the DEEP. In the agreement, CL&P agreed to forego rate recovery of $40 million of the deferred storm restoration costs associated with restoration activities following Tropical Storm Irene and the October 2011 snowstorm. On April 2, 2012, the PURA approved the settlement agreement and the merger of NU and NSTAR.
CY2012	nu	Customer Rate Credits For Business Combination CustomerRateCreditsForBusinessCombination	46000000	USD
CY2012	nu	Storm Cost Deferral Reduction StormCostDeferralReduction	40000000	USD
CY2012	nu	Establishment Of Energy Efficiency Fund EstablishmentOfEnergyEfficiencyFund	15000000	USD
CY2012	nu	Total Pre Tax Settlement Agreement Impacts TotalPreTaxSettlementAgreementImpacts	101000000	USD
CY2011Q4	us-gaap	Goodwill Goodwill	300000000	USD
CY2013Q4	us-gaap	Regulatory Assets RegulatoryAssets	4294500000	USD
CY2012Q4	us-gaap	Regulatory Assets RegulatoryAssets	5837400000	USD
CY2013Q4	nu	Electric And Natural Gas Utility Accumulated Depreciation ElectricAndNaturalGasUtilityAccumulatedDepreciation	5387000000	USD
CY2013Q4	nu	Other Accumulated Depreciation OtherAccumulatedDepreciation	196200000	USD
CY2013Q4	us-gaap	Public Utilities Property Plant And Equipment Accumulated Depreciation PublicUtilitiesPropertyPlantAndEquipmentAccumulatedDepreciation	5583200000	USD
CY2013	nu	Description Of Accumulated Equity Return DescriptionOfAccumulatedEquityReturn	Equity Return on Regulatory Assets: For rate-making purposes, the Regulated companies recover the carrying cost related to their regulatory assets. For certain regulatory assets, the carrying cost recovered includes an equity return component. This equity return, which is not recorded on the balance sheets, totaled $1.9 million and $2.5 million for CL&P and $33.1 million and $21.8 million for PSNH as of December 31, 2013 and 2012, respectively. These carrying costs will be recovered from customers in future rates.
CY2013	us-gaap	Description Of Regulatory Assets And Liabilities DescriptionOfRegulatoryAssetsAndLiabilities	Regulatory Assets - The following provides further information about regulatory assets: Benefit Costs: NU's Pension, SERP and PBOP Plans are accounted for in accordance with accounting guidance on defined benefit pension and other postretirement plans. Because the Regulated companies recover the retiree benefit costs from customers through rates, regulatory assets are recorded in lieu of a charge to Accumulated Other Comprehensive Income/(Loss) to reflect the liability that is recognized for the funded status of the pension and other postretirement plans and is remeasured annually. Regulatory accounting was also applied to the portions of NU's service company costs that support the Regulated companies, as these amounts are also recoverable. CL&P, NSTAR Electric, PSNH and WMECO do not collect carrying charges on these benefit costs regulatory assets. CL&P, NSTAR Electric, PSNH and WMECO recover benefit costs related to their distribution and transmission operations from customers in rates as allowed by their applicable regulatory commissions. NSTAR Electric and WMECO each recover their qualified pension and postretirement expenses related to distribution operations through rate reconciling mechanisms that fully track the change in net pension and postretirement expenses each year. NSTAR Electric earns a carrying charge on the excess cumulative benefit plan trust fund contributions it has made over what it has cumulatively recognized as net periodic benefit expense, net of deferred income taxes. As of December 31, 2013 and 2012, these balances were $379.9 million and $366.8 million of the total benefit costs regulatory asset, respectively. Derivative Liabilities: Regulatory assets recorded as an offset to derivative liabilities relate to the fair value of contracts used to purchase energy and energy-related products that will be recovered from customers in future rates. See Note 5, "Derivative Instruments," to the financial statements for further information.  These assets are excluded from rate base and are being recovered as the actual settlements occur over the duration of the contracts. Goodwill: The goodwill regulatory asset originated from the transaction that created NSTAR in 1999. This regulatory asset is currently being amortized and recovered from customers in rates without a carrying charge over a 40-year period (as of December 31, 2013, there were 26 years of amortization remaining). Storm Restoration Costs: The storm restoration cost deferrals relate to costs incurred at CL&P, NSTAR Electric, PSNH and WMECO that each company expects to recover from customers. A storm must meet certain criteria to be declared a major storm with the criteria specific to each state jurisdiction and utility company as follows: Connecticut - qualifying storm restoration costs must exceed $5 million for a storm to be declared a major storm; Massachusetts - qualifying storm restoration costs must exceed $1 million for NSTAR Electric and $300,000 for WMECO and an emergency response plan must be initiated for a storm to be declared a major storm; and New Hampshire - For a storm to be declared a major storm: (1) at least 10 percent of customers must be without power with at least 200 concurrent locations requiring repairs (trouble spots), or (2) at least 300 concurrent trouble spots must be reported. Once a storm is declared major, all qualifying expenses prudently incurred during storm restoration efforts are deferred and recovered from customers. In addition to storm restoration costs, PSNH is allowed recovery of prudently incurred storm pre-staging costs in accordance with NHPUC regulation. In 2013, 2012 and 2011, CL&P, NSTAR Electric, PSNH and WMECO experienced significant storms, including Tropical Storm Irene, the October 2011 snowstorm, Storm Sandy, and the February 2013 blizzard. As a result of these storm events, each Company suffered extensive damage to its distribution and transmission systems resulting in customer outages, which required the incurrence of costs to repair damage and restore customer service. The storm restoration cost regulatory asset balance at CL&P, NSTAR Electric, PSNH and WMECO reflects costs incurred for major storm events. Management believes the storm restoration costs were prudent and meet the criteria for specific cost recovery in Connecticut, Massachusetts and New Hampshire and as a result, are probable of recovery. Storm Filings: Each electric utility is seeking recovery of its deferred storm restoration costs through its applicable regulatory recovery process. On February 3, 2014, the PURA issued a draft decision on CL&P’s request to recover storm restoration costs associated with five major storms, all of which occurred in 2011 and 2012. In its draft decision, the PURA approved recovery of $365 million of deferred storm restoration costs and ordered CL&P to capitalize approximately $18 million of the deferred storm restoration costs as utility plant, which will be included in depreciation expense in future rate proceedings. PURA will allow recovery of the $365 million with carrying charges in CL&P’s distribution rates over a six-year period beginning December 1, 2014. The remaining costs were either disallowed or are probable of recovery in future rates and did not have a material impact on CL&P’s financial position, results of operations or cash flows. On December 30, 2013, the DPU approved NSTAR Electric’s request to recover storm restoration costs, plus carrying costs, related to Tropical Storm Irene and the October 2011 snowstorm. The DPU approved recovery of $34.2 million of the $38 million requested costs. NSTAR Electric will recover these costs, plus carrying costs, in its distribution rates over a five-year period beginning on January 1, 2014. On June 27, 2013, the NHPUC approved an increase to PSNH’s distribution rates effective July 1, 2013, which included a $5 million increase to the current level of funding for the major storm cost reserve. The major storm cost reserve is used to offset the storm restoration cost regulatory asset. On August 30, 2013, WMECO submitted its 2013 Annual SRRCA filing to begin recovering the restoration costs associated with the October 2011 snowstorm and Storm Sandy. On December 20, 2013, the DPU approved the 2013 Annual SRRCA filing for effect on January 1, 2014, subject to further review and reconciliation. Income Taxes, Net: The tax effect of temporary book-tax differences (differences between the periods in which transactions affect income in the financial statements and the periods in which they affect the determination of taxable income, including those differences relating to uncertain tax positions) is accounted for in accordance with the rate-making treatment of the applicable regulatory commissions and accounting guidance for income taxes. Differences in income taxes between the accounting guidance and the rate-making treatment of the applicable regulatory commissions are recorded as regulatory assets. As these assets are offset by deferred income tax liabilities, no carrying charge is collected. For further information regarding income taxes, see Note 11, "Income Taxes," to the financial statements. Securitized Assets: NSTAR Electric's securitized regulatory asset balance primarily included costs related to purchase power contract divestitures and certain costs related to NSTAR Electric’s former generation business that were recovered with a return through the transition charge and amounted to $186.1 million as of December 31, 2012. These costs were fully recovered from customers in 2013. The securitized regulatory asset balance as of December 31, 2012 also included proceeds received from the issuance of RRBs at NSTAR Electric, PSNH and WMECO that were used to buy out or buy down purchase power contracts. The collateralized amounts reflected as securitized regulatory assets for NSTAR Electric, PSNH and WMECO as of December 31, 2012 were $14.1 million, $19.7 million and $7.8 million, respectively. As of December 31, 2013, NSTAR Electric's, PSNH's and WMECO's RRBs were fully redeemed and the related regulatory assets were fully recovered from customers. Contractual Obligations - Yankee Companies: CL&P, NSTAR Electric, PSNH and WMECO are responsible for their proportionate share of the remaining costs of the CYAPC, YAEC and MYAPC nuclear facilities, including decommissioning. A portion of these amounts was recorded as a regulatory asset. Amounts for CL&P are earning a return and are being recovered through the CTA. Amounts for NSTAR Electric and WMECO are being recovered without a return through the transition charge. Amounts for PSNH were fully recovered in 2006. As a result of NU's consolidation of CYAPC and YAEC, NU's regulatory asset balance also includes the regulatory assets of CYAPC and YAEC, which totalled $129.8 million and $214 million as of December 31, 2013 and 2012, respectively. At the NU consolidated level, intercompany transactions between CL&P, NSTAR Electric, PSNH and WMECO and the CYAPC and YAEC companies have been eliminated in consolidation. Buy Out Agreements for Power Contracts: NSTAR Electric's balance represents the contract termination liability related to certain purchase power contract buy out agreements that were executed in 2004. The contracts’ termination payments occur through September 2016 and are collected from customers through NSTAR Electric’s transition charge over the same period. Therefore, NSTAR Electric does not earn a return on this regulatory asset. PSNH's balance represents payments associated with the termination of various power purchase contracts that were recorded as regulatory assets and are amortized over the remaining life of the contracts. Regulatory Tracker Mechanisms: The Regulated companies’ approved rates are designed to recover their incurred costs to provide service to customers. The Regulated companies are permitted to recover certain of their costs on a fully-reconciling basis through regulatory commission-approved tracking mechanisms. The difference between the costs incurred (or the rate recovery allowed) and the actual revenues is recorded as regulatory assets (for undercollections) or regulatory liabilities (for overcollections) to be included in future customer rates each year. Carrying charges are recorded on all material regulatory tracker mechanisms. CL&P, NSTAR Electric, PSNH and WMECO each recover the costs associated with the procurement of energy, transmission related costs from FERC-approved transmission tariffs, energy efficiency programs, low income assistance programs, and restructuring and stranded costs as a result of deregulation, on a fully reconciling basis. Energy procurement costs at PSNH include the costs related to its generating stations. WMECO’s distribution revenue is decoupled from its customer sales volume. WMECO reconciles its annual base distribution rate recovery to a pre-established level of baseline distribution delivery service revenue. Any difference between the allowed level of distribution revenue and the actual amount incurred in a calendar year is adjusted through rates in the following year. Other Regulatory Assets: Other Regulatory Assets primarily include asset retirement obligations, environmental remediation costs, losses associated with the reacquisition or redemption of long-term debt and various other items, partially offset by purchase price adjustments recorded as Regulatory Assets in connection with the merger with NSTAR. The ARO costs associated with the depreciation of the Regulated companies' ARO assets and accretion of the ARO liabilities are recorded as regulatory assets. For CL&P, NSTAR Electric and WMECO, ARO assets, regulatory assets and liabilities offset and are excluded from rate base. PSNH's ARO assets, regulatory assets and liabilities are included in rate base; these costs are being recovered over the life of the underlying property, plant and equipment. Cost of Removal: NU's Regulated companies currently recover amounts in rates for future costs of removal of plant assets over the lives of the assets. The estimated cost to remove utility assets from service is recognized as a component of depreciation expense and the cumulative amounts collected from customers but not yet expended is recognized as a regulatory liability. Expended costs that exceed amounts collected from customers are recognized as regulatory assets, as they are probable of recovery in future rates. AFUDC - Transmission: AFUDC was recorded by CL&P and WMECO for their NEEWS projects through May 31, 2011, all of which was reserved as a regulatory liability to reflect rate base recovery for 100 percent of the CWIP as a result of FERC-approved transmission incentives. Effective June 1, 2011, FERC approved changes to the ISO-NE Tariff in order to include 100 percent of the NEEWS CWIP in regional rate base. As a result, CL&P and WMECO no longer record AFUDC on NEEWS CWIP. NSTAR Electric recorded AFUDC on reliability-related projects over $5 million through December 31, 2013, 50 percent of which was recorded as a regulatory liability to reflect rate base recovery for 50 percent of the CWIP as a result of FERC-approved transmission incentives. Other Regulatory Liabilities: Other Regulatory Liabilities primarily includes amounts that are subject to various rate reconciling mechanisms that, as of each period end date, would result in refunds to customers.
CY2013	us-gaap	Description Of Regulatory Costs Not Yet Approved DescriptionOfRegulatoryCostsNotYetApproved	Regulatory Costs in Other Long-Term Assets: The Regulated companies had $65.1 million ($7.3 million for CL&P, $33.4 million for NSTAR Electric, and $10.1 million for WMECO) and $69.9 million ($3.9 million for CL&P, $25.4 million for NSTAR Electric, $35.7 million for PSNH, and $1.4 million for WMECO) of additional regulatory costs as of December 31, 2013 and 2012, respectively, that were included in Other Long-Term Assets on the balance sheets. These amounts represent incurred costs for which recovery has not yet been specifically approved by the applicable regulatory agency. However, based on regulatory policies or past precedent on similar costs, management believes it is probable that these costs will ultimately be approved and recovered from customers in rates. The PSNH balance as of December 31, 2012 primarily related to storm restoration costs incurred for Tropical Storm Irene, the October 2011 snowstorm and Storm Sandy that met the NHPUC criteria for cost deferral and recovery. Refer to the "Storm Restoration Costs" section in this Note for further discussion. The NSTAR Electric balance as of December 31, 2013 and 2012 primarily related to costs deferred in connection with the basic service bad debt adder. See Note 12G, "Commitments and Contingencies – Basic Service Bad Debt Adder," for further information.
CY2013Q4	us-gaap	Regulatory Liabilities RegulatoryLiabilities	707300000	USD
CY2012Q4	us-gaap	Regulatory Liabilities RegulatoryLiabilities	674300000	USD
CY2013	us-gaap	Property Plant And Equipment Depreciation Methods PropertyPlantAndEquipmentDepreciationMethods	Utility property, plant and equipment is recorded at original cost. Original cost includes materials, labor, construction overhead and AFUDC for regulated property. The cost of repairs and maintenance, including planned major maintenance activities, is charged to Operating Expenses as incurred. Depreciation of utility assets is calculated on a straight-line basis using composite rates based on the estimated remaining useful lives of the various classes of property (estimated useful life for PSNH distribution). The composite rates are subject to approval by the appropriate state regulatory agency. The composite rates include a cost of removal component, which is collected from customers over the lives of the plant assets and is recognized as a regulatory liability. Depreciation rates are applied to property from the time it is placed in service. Upon retirement from service, the cost of the utility asset is charged to the accumulated provision for depreciation. The actual incurred removal costs are applied against the related regulatory liability.
CY2013Q4	us-gaap	Public Utilities Property Plant And Equipment Distribution PublicUtilitiesPropertyPlantAndEquipmentDistribution	11950200000	USD
CY2013Q4	nu	Public Utilities Property Plant And Equipment Distribution Natural Gas PublicUtilitiesPropertyPlantAndEquipmentDistributionNaturalGas	2425900000	USD
CY2013Q4	us-gaap	Public Utilities Property Plant And Equipment Transmission PublicUtilitiesPropertyPlantAndEquipmentTransmission	6412500000	USD
CY2013Q4	us-gaap	Public Utilities Property Plant And Equipment Generation Or Processing PublicUtilitiesPropertyPlantAndEquipmentGenerationOrProcessing	1152300000	USD
CY2013Q4	nu	Public Utilities Property Plant And Equipment Electric And Natural Gas Utility Total PublicUtilitiesPropertyPlantAndEquipmentElectricAndNaturalGasUtilityTotal	21940900000	USD
CY2013Q4	us-gaap	Public Utilities Property Plant And Equipment Other Property Plant And Equipment PublicUtilitiesPropertyPlantAndEquipmentOtherPropertyPlantAndEquipment	508700000	USD
CY2013Q4	us-gaap	Public Utilities Property Plant And Equipment Plant In Service PublicUtilitiesPropertyPlantAndEquipmentPlantInService	22449600000	USD
CY2013Q4	nu	Property Plant And Equipment Net Excluding Construction Work In Progress PropertyPlantAndEquipmentNetExcludingConstructionWorkInProgress	16866400000	USD
CY2013Q4	us-gaap	Public Utilities Property Plant And Equipment Construction Work In Progress PublicUtilitiesPropertyPlantAndEquipmentConstructionWorkInProgress	709800000	USD
CY2012Q4	us-gaap	Public Utilities Property Plant And Equipment Distribution PublicUtilitiesPropertyPlantAndEquipmentDistribution	11438200000	USD
CY2012Q4	nu	Public Utilities Property Plant And Equipment Distribution Natural Gas PublicUtilitiesPropertyPlantAndEquipmentDistributionNaturalGas	2274200000	USD
CY2012Q4	us-gaap	Public Utilities Property Plant And Equipment Transmission PublicUtilitiesPropertyPlantAndEquipmentTransmission	5541100000	USD
CY2012Q4	us-gaap	Public Utilities Property Plant And Equipment Generation Or Processing PublicUtilitiesPropertyPlantAndEquipmentGenerationOrProcessing	1146600000	USD
CY2012Q4	nu	Public Utilities Property Plant And Equipment Electric And Natural Gas Utility Total PublicUtilitiesPropertyPlantAndEquipmentElectricAndNaturalGasUtilityTotal	20400100000	USD
CY2012Q4	us-gaap	Public Utilities Property Plant And Equipment Other Property Plant And Equipment PublicUtilitiesPropertyPlantAndEquipmentOtherPropertyPlantAndEquipment	429300000	USD
CY2012Q4	us-gaap	Public Utilities Property Plant And Equipment Plant In Service PublicUtilitiesPropertyPlantAndEquipmentPlantInService	20829400000	USD
CY2012Q4	nu	Electric And Natural Gas Utility Accumulated Depreciation ElectricAndNaturalGasUtilityAccumulatedDepreciation	5065100000	USD
CY2012Q4	nu	Other Accumulated Depreciation OtherAccumulatedDepreciation	171500000	USD
CY2012Q4	us-gaap	Public Utilities Property Plant And Equipment Accumulated Depreciation PublicUtilitiesPropertyPlantAndEquipmentAccumulatedDepreciation	5236600000	USD
CY2012Q4	nu	Property Plant And Equipment Net Excluding Construction Work In Progress PropertyPlantAndEquipmentNetExcludingConstructionWorkInProgress	15592800000	USD
CY2012Q4	us-gaap	Public Utilities Property Plant And Equipment Construction Work In Progress PublicUtilitiesPropertyPlantAndEquipmentConstructionWorkInProgress	1012200000	USD
CY2012	us-gaap	Public Utilities Property Plant And Equipment Disclosure Of Composite Depreciation Rate For Plants In Service PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService	0.025	pure
CY2011	us-gaap	Public Utilities Property Plant And Equipment Disclosure Of Composite Depreciation Rate For Plants In Service PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService	0.026	pure
CY2013Q4	nu	Distribution Assets Average Useful Life DistributionAssetsAverageUsefulLife	36.1	pure
CY2013Q4	nu	Transmission Assets Average Useful Life TransmissionAssetsAverageUsefulLife	43.0	pure
CY2013Q4	nu	Generation Assets Average Useful Life GenerationAssetsAverageUsefulLife	32.2	pure
CY2013Q4	nu	Other Assets Average Useful Life OtherAssetsAverageUsefulLife	14.6	pure
CY2013Q4	nu	Current Derivative Assets Consolidated CurrentDerivativeAssetsConsolidated	10200000	USD
CY2013Q4	nu	Consolidated Current Derivative Liabilities ConsolidatedCurrentDerivativeLiabilities	93700000	USD
CY2012Q4	nu	Current Derivative Assets Consolidated CurrentDerivativeAssetsConsolidated	11400000	USD
CY2012Q4	nu	Consolidated Current Derivative Liabilities ConsolidatedCurrentDerivativeLiabilities	117200000	USD
CY2013Q4	nu	Derivative Assets Subject To Credit Risk With Investment Grade Counterparty DerivativeAssetsSubjectToCreditRiskWithInvestmentGradeCounterparty	80000000	USD
CY2013	us-gaap	Description Of Derivative Activity Volume DescriptionOfDerivativeActivityVolume	As of December 31, 2013 and 2012, NU had NYMEX future contracts in order to reduce variability associated with the purchase price of approximately 9.1 million and 11.5 million MMBtu of natural gas, respectively. As of December 31, 2012, NU had approximately 24 thousand MWh of supply volumes remaining in its unregulated wholesale portfolio when expected sales were compared with supply contracts. These contracts expired on December 31, 2013.
CY2012Q4	us-gaap	Derivative Collateral Right To Reclaim Cash DerivativeCollateralRightToReclaimCash	4100000	USD
CY2013Q4	us-gaap	Additional Collateral Aggregate Fair Value AdditionalCollateralAggregateFairValue	0	USD
CY2013Q4	us-gaap	Derivative Net Liability Position Aggregate Fair Value DerivativeNetLiabilityPositionAggregateFairValue	0	USD
CY2012Q4	us-gaap	Derivative Net Liability Position Aggregate Fair Value DerivativeNetLiabilityPositionAggregateFairValue	15300000	USD
CY2012Q4	us-gaap	Collateral Already Posted Aggregate Fair Value CollateralAlreadyPostedAggregateFairValue	0	USD
CY2012Q4	us-gaap	Additional Collateral Aggregate Fair Value AdditionalCollateralAggregateFairValue	17400000	USD
CY2013	nu	Fairvalueinputsexitpricepremium Fairvalueinputsexitpricepremium	Exit price premiums of 10 percent through 32 percent are also applied on these contracts and reflect the most recent market activity available for similar type contracts.
CY2011Q4	us-gaap	Fair Value Measurement With Unobservable Inputs Reconciliations Recurring Basis Liability Value FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue	962200000	USD
CY2012	us-gaap	Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Liability Settlements FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements	75100000	USD
CY2012Q4	us-gaap	Fair Value Measurement With Unobservable Inputs Reconciliations Recurring Basis Liability Value FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue	878600000	USD
CY2013Q4	us-gaap	Fair Value Measurement With Unobservable Inputs Reconciliations Recurring Basis Liability Value FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue	635200000	USD
CY2013	us-gaap	Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Liability Gain Loss Included In Earnings FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings	10900000	USD
CY2013	nu	Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Reg Asset Liability FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetLiabilityGainLossIncludedInRegAssetLiability	158300000	USD
CY2013	us-gaap	Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Liability Settlements FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements	74200000	USD
CY2012	nu	Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Reg Asset Liability FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetLiabilityGainLossIncludedInRegAssetLiability	-29200000	USD
CY2012	us-gaap	Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Liability Gain Loss Included In Earnings FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings	10900000	USD
CY2012	nu	Derivativeliabilityrecordedatmergerdatelevel3 Derivativeliabilityrecordedatmergerdatelevel3	-5400000	USD
CY2012	us-gaap	Fair Value Measurement With Unobservable Inputs Reconciliation Liability Transfers Out Of Level3 FairValueMeasurementWithUnobservableInputsReconciliationLiabilityTransfersOutOfLevel3	32200000	USD
CY2012Q4	nu	Fair Value Of Securities Under Fair Value Option FairValueOfSecuritiesUnderFairValueOption	47000000	USD
CY2012	us-gaap	Fair Value Option Changes In Fair Value Gain Loss1 FairValueOptionChangesInFairValueGainLoss1	5900000	USD
CY2013Q4	nu	Fair Value Of Securities Under Fair Value Option FairValueOfSecuritiesUnderFairValueOption	57200000	USD
CY2013	us-gaap	Fair Value Option Changes In Fair Value Gain Loss1 FairValueOptionChangesInFairValueGainLoss1	10200000	USD
CY2013Q4	us-gaap	Marketable Securities Restricted Noncurrent MarketableSecuritiesRestrictedNoncurrent	424000000	USD
CY2012Q4	us-gaap	Marketable Securities Restricted Noncurrent MarketableSecuritiesRestrictedNoncurrent	340400000	USD
CY2013Q4	us-gaap	Available For Sale Securities Debt Maturities Within One Year Amortized Cost AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost	72400000	USD
CY2013Q4	us-gaap	Available For Sale Securities Debt Maturities After One Through Five Years Amortized Cost AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost	62100000	USD
CY2013Q4	us-gaap	Available For Sale Securities Debt Maturities After Five Through Ten Years Amortized Cost AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost	59400000	USD
CY2013Q4	us-gaap	Available For Sale Securities Debt Maturities After Ten Years Amortized Cost AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost	105300000	USD
CY2013Q4	us-gaap	Available For Sale Securities Debt Maturities Amortized Cost AvailableForSaleSecuritiesDebtMaturitiesAmortizedCost	299200000	USD
CY2013Q4	us-gaap	Available For Sale Securities Debt Maturities Within One Year Fair Value AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue	72300000	USD
CY2013Q4	us-gaap	Available For Sale Securities Debt Maturities After One Through Five Years Fair Value AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue	62700000	USD
CY2013Q4	us-gaap	Available For Sale Securities Debt Maturities After Five Through Ten Years Fair Value AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue	59300000	USD
CY2013Q4	us-gaap	Available For Sale Securities Debt Maturities After Ten Years Fair Value AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue	105300000	USD
CY2013Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	299600000	USD
CY2013Q4	us-gaap	Investments Fair Value Disclosure InvestmentsFairValueDisclosure	580900000	USD
CY2012Q4	us-gaap	Investments Fair Value Disclosure InvestmentsFairValueDisclosure	492300000	USD
CY2013	us-gaap	Asset Retirement Obligation Liabilities Settled AssetRetirementObligationLiabilitiesSettled	-13800000	USD
CY2013	us-gaap	Asset Retirement Obligation Accretion Expense AssetRetirementObligationAccretionExpense	23800000	USD
CY2013	us-gaap	Asset Retirement Obligation Revision Of Estimate AssetRetirementObligationRevisionOfEstimate	2600000	USD
CY2013Q4	us-gaap	Asset Retirement Obligation AssetRetirementObligation	424900000	USD
CY2011Q4	us-gaap	Asset Retirement Obligation AssetRetirementObligation	56200000	USD
CY2012	us-gaap	Asset Retirement Obligation Liabilities Incurred AssetRetirementObligationLiabilitiesIncurred	1500000	USD
CY2012	us-gaap	Asset Retirement Obligation Accretion Expense AssetRetirementObligationAccretionExpense	20200000	USD
CY2012	us-gaap	Asset Retirement Obligation Revision Of Estimate AssetRetirementObligationRevisionOfEstimate	21400000	USD
CY2012Q4	us-gaap	Asset Retirement Obligation AssetRetirementObligation	412200000	USD
CY2012	us-gaap	Asset Retirement Obligation Liabilities Settled AssetRetirementObligationLiabilitiesSettled	-7200000	USD
CY2012Q4	nu	Liability Assumed Upon Consolidation Of Cyapc And Yaec LiabilityAssumedUponConsolidationOfCyapcAndYaec	284200000	USD
CY2012Q4	nu	Liability Assumed Upon Merger With Nstar LiabilityAssumedUponMergerWithNstar	35900000	USD
CY2013	us-gaap	Asset Retirement Obligation Liabilities Incurred AssetRetirementObligationLiabilitiesIncurred	100000	USD
CY2013	nu	Short Term Debt Regulatory Limits ShortTermDebtRegulatoryLimits	The amount of short-term borrowings that may be incurred by CL&P, NSTAR Electric and WMECO is subject to periodic approval by the FERC. On July 31, 2013, the FERC granted authorization to allow CL&P and WMECO to incur total short-term borrowings up to a maximum of $600 million and $300 million, respectively, effective January 1, 2014 through December 31, 2015. On May 16, 2012, the FERC granted authorization to allow NSTAR Electric to issue total short-term debt securities in an aggregate principal amount not to exceed $655 million outstanding at any one time, effective October 23, 2012 through October 23, 2014. As a result of the NHPUC having jurisdiction over PSNH's short-term debt, PSNH is not currently required to obtain FERC approval for its short-term borrowings. CL&P's certificate of incorporation contains preferred stock provisions restricting the amount of unsecured debt that CL&P may incur, including limiting unsecured indebtedness with a maturity of less than 10 years to 10 percent of total capitalization. In November 2003, CL&P obtained from its preferred stockholders a waiver of such 10 percent limit for a ten-year period expiring in March 2014, provided that all unsecured indebtedness does not exceed 20 percent of total capitalization. As of December 31, 2013, CL&P had $776.9 million of unsecured debt capacity available under this authorization.
CY2013	nu	Description Of Commercial Paper Program DescriptionOfCommercialPaperProgram	NU parent, CL&P, PSNH, WMECO, NSTAR Gas and Yankee Gas are parties to a five-year revolving credit facility. The revolving credit facility is to be used primarily to backstop the commercial paper program at NU, which commenced July 25, 2012. The commercial paper program allows NU parent to issue commercial paper as a form of short-term debt. On September 6, 2013, the $1.15 billion revolving credit facility dated July 25, 2012 was amended to increase the aggregate principal amount available thereunder by $300 million to $1.45 billion, to extend the expiration date from July 25, 2017 to September 6, 2018, and to increase CL&P's borrowing sublimit from $300 million to $600 million. PSNH and WMECO each have borrowing sublimits of $300 million. On September 6, 2013, NU parent’s $1.15 billion commercial paper program was increased by $300 million to $1.45 billion. NSTAR Electric has a five-year $450 million revolving credit facility. This facility serves to backstop NSTAR Electric’s existing $450 million commercial paper program. On September 6, 2013, NSTAR Electric amended its revolving credit facility dated July 25, 2012 to extend the expiration date from July 25, 2017 to September 6, 2018.
CY2013	nu	Description Of St Debt Reclassified To Lt DescriptionOfStDebtReclassifiedToLt	On January 2, 2014, Yankee Gas issued $100 million of Series L First Mortgage Bonds. A portion of the proceeds was used to pay short-term borrowings outstanding under the NU commercial paper program. As a result and in accordance with applicable accounting guidance, $25 million of the NU commercial paper program borrowings have been classified as Long-Term Debt as of December 31, 2013.
CY2012	nu	Description Of St Debt Reclassified To Lt DescriptionOfStDebtReclassifiedToLt	As of December 31, 2012, CL&P had $89 million in borrowings outstanding under this credit agreement with a weighted average interest rate of 3.325 percent.
CY2013	nu	Description Of Working Capital DescriptionOfWorkingCapital	Each of NU, CL&P, NSTAR Electric, PSNH and WMECO use its available capital resources to fund its respective construction expenditures, meet debt requirements, pay operating costs, including storm-related costs, pay dividends and fund other corporate obligations, such as pension contributions. The current growth in NU’s transmission construction expenditures utilizes a significant amount of cash for projects that have a long-term return on investment and recovery period. In addition, NU’s Regulated companies recover its electric and natural gas distribution construction expenditures as the related project costs are depreciated over the life of the assets. This impacts the timing of the revenue stream designed to fully recover the total investment plus a return on the equity portion of the cost and related financing costs. These factors have resulted in current liabilities exceeding current assets by approximately $1.2 billion, $398 million and $339 million at NU, CL&P and NSTAR Electric, respectively, as of December 31, 2013.As of December 31, 2013, $501.7 million of NU's obligations classified as current liabilities relates to long-term debt that will be paid in the next 12 months, consisting of $150 million for CL&P, $301.7 million for NSTAR Electric and $50 million for PSNH. In addition, $31.7 million relates to the amortization of the purchase accounting fair value adjustment that will be amortized in the next twelve months. NU, with its strong credit ratings, has several options available in the financial markets to repay or refinance these maturities with the issuance of new long-term debt. NU, CL&P, NSTAR Electric, PSNH and WMECO will reduce their short-term borrowings with cash received from operating cash flows or with the issuance of new long-term debt, determined considering capital requirements and maintenance of NU's credit rating and profile. Management expects the future operating cash flows of NU, CL&P, NSTAR Electric, PSNH and WMECO, along with the access to financial markets, will be sufficient to meet any future operating requirements and capital investment forecasted opportunities.
CY2013	us-gaap	Long Term Debt Description LongTermDebtDescription	On January 15, 2013, CL&P issued $400 million of 2.50 percent Series A First and Refunding Mortgage Bonds with a maturity date of January 15, 2023. The proceeds, net of issuance costs, were used to pay short-term borrowings outstanding under the CL&P credit agreement of $89 million and the NU commercial paper program of $305.8 million. As a result and in accordance with applicable accounting guidance, these amounts were classified as Long-Term Debt on the balance sheet as of December 31, 2012. In April 2012, CL&P remarketed $62 million of tax-exempt PCRBs for a three-year period. The PCRBs, which mature on May 1, 2031, carry a coupon rate of 1.55 percent during the current three-year fixed rate period and are subject to mandatory tender for purchase on April 1, 2015. On September 3, 2013, CL&P redeemed at par $125 million of 1.25 percent Series B 2011 PCRBs, which were subject to mandatory tender for purchase, using short-term debt. On May 17, 2013, NSTAR Electric issued $200 million of three-year floating rate debentures due in May 2016. The proceeds, net of issuance costs, were used to repay commercial paper borrowings and for general corporate purposes. The debentures have a coupon rate reset quarterly based on 3-month LIBOR plus a credit spread of 0.24 percent. The interest rate as of December 31, 2013 was 0.478 percent. On May 1, 2013, PSNH redeemed at par approximately $109 million of the 2001 Series C PCRBs that were due to mature in 2021 using short-term debt. On November 14, 2013, PSNH issued $250 million of 3.50 percent Series S First Mortgage Bonds due in 2023. On December 23, 2013, PSNH redeemed approximately $89 million of the Series B PCRBs that were due to mature in 2021. The proceeds of the Series S issuance were used to repay the short term debt used to redeem the $109 million 2001 Series C PCRBs and to redeem the $89 million Series B PCRBs and pay the associated call premium. The remaining proceeds of the offering were used to refinance short-term debt. On September 1, 2013, WMECO repaid at maturity the $55 million Series A Senior Notes using short-term debt. On November 15, 2013, WMECO issued $80 million of 3.88 percent Series G Senior Notes due in 2023. The proceeds, net of issuance costs, were used to pay short-term borrowings and for other working capital purposes. On January 2, 2014, Yankee Gas issued $100 million of 4.82 percent Series L First Mortgage Bonds due to mature in 2044. The proceeds, net of issuance costs, were used to repay the Series G $75 million First Mortgage Bonds that matured on January 1, 2014 and to pay $25 million in short-term borrowings. As a result and in accordance with applicable accounting guidance, these amounts were classified as Long-Term Debt on NU’s balance sheet as of December 31, 2013. On May 13, 2013, NU parent issued $750 million of Senior Notes, consisting of $300 million of 1.45 percent Series E Senior Notes due to mature in 2018 and $450 million of 2.80 percent Series F Senior Notes due to mature in 2023. The proceeds, net of issuance costs, were used to repay the NU parent $250 million Series C Senior Notes at a coupon rate of 5.65 percent that matured on June 1, 2013 and the NU parent $300 million floating rate Series D Senior Notes that matured on September 20, 2013. The remaining net proceeds were used to repay commercial paper program borrowings and for working capital purposes. The DOE is responsible for the selection and development of repositories for, and the disposal of, spent nuclear fuel and high-level radioactive waste. For nuclear fuel used to generate electricity prior to April 7, 1983 (Prior Period Spent Nuclear Fuel) for CL&P and WMECO, an accrual has been recorded for the full liability, and payment must be made by CL&P and WMECO to the DOE prior to the first delivery of spent fuel to the DOE. After the sale of Millstone, CL&P and WMECO remained responsible for their share of the disposal costs associated with the Prior Period Spent Nuclear Fuel. Until such payment to the DOE is made, the outstanding liability will continue to accrue interest at the 3-month Treasury bill yield rate. In addition, as a result of consolidating CYAPC, NU has consolidated $179.4 million in additional spent nuclear fuel obligations, including interest, as of December 31, 2013. Fees due to the DOE for the disposal of CL&P's and WMECO's Prior Period Spent Nuclear Fuel and CYAPC's spent nuclear fuel obligation include accumulated interest costs of $350.3 million and $350 million ($177.9 million and $177.8 million for CL&P and $41.7 million and $41.7 million for WMECO) as of December 31, 2013 and 2012, respectively.
CY2013Q4	us-gaap	Long Term Debt Maturities Repayments Of Principal In Next Twelve Months LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths	576700000	USD
CY2013Q4	us-gaap	Long Term Debt Maturities Repayments Of Principal In Year Two LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo	216700000	USD
CY2013Q4	us-gaap	Long Term Debt Maturities Repayments Of Principal In Year Three LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree	200000000	USD
CY2013Q4	us-gaap	Long Term Debt Maturities Repayments Of Principal In Year Four LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour	745000000	USD
CY2013Q4	us-gaap	Long Term Debt Maturities Repayments Of Principal In Year Five LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive	810000000	USD
CY2013Q4	us-gaap	Long Term Debt Maturities Repayments Of Principal After Year Five LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive	5031600000	USD
CY2013Q4	nu	Longtermdebtmaturitiesrepaymentsofprincipaltotal Longtermdebtmaturitiesrepaymentsofprincipaltotal	7580000000	USD
CY2012	us-gaap	Defined Contribution Plan Cost Recognized DefinedContributionPlanCostRecognized	25700000	USD
CY2013	nu	Description Of Allocation Of Assets To Subsidiaries DescriptionOfAllocationOfAssetsToSubsidiaries	Effective January 1, 2013, the NSTAR Pension Plan assets were transferred into the NUSCO Pension Plan master trust. The, NUSCO Pension Plan is entitled to approximately 66 percent of each asset category in the master trust, the NSTAR Pension Plan is entitled to approximately 30 percent of each asset category in the master trust and the 401(h) plans are entitled to approximately four percent of each asset category in the master trust. CL&P, PSNH and WMECO participate in the NUSCO Pension and PBOP Plans. Each company participating in the plans is allocated a portion of the total plan assets. As of December 31, 2013 and 2012, the NUSCO Pension Plan had total assets of $2,750.4 million and $2,342.6 million, respectively. CL&P’s, PSNH’s and WMECO’s portion of these total Pension Plan assets was 37 percent, 19 percent and 9 percent, respectively, as of December 31, 2013, and 40 percent, 17 percent and 9 percent, respectively, as of December 31, 2012. The NUSCO PBOP Plans had total assets of $391 million and $334.9 million as of December 31, 2013 and 2012, respectively. CL&P’s, PSNH’s and WMECO’s portion of these total PBOP Plan assets was 39 percent, 21 percent and 9 percent, respectively, as of December 31, 2013 and 2012.
CY2013	us-gaap	Defined Contribution Plan Cost Recognized DefinedContributionPlanCostRecognized	37000000	USD
CY2011	us-gaap	Defined Contribution Plan Cost Recognized DefinedContributionPlanCostRecognized	17400000	USD
CY2013	us-gaap	Employee Stock Ownership Plan Esop Compensation Expense EmployeeStockOwnershipPlanESOPCompensationExpense	9100000	USD
CY2012	us-gaap	Employee Stock Ownership Plan Esop Compensation Expense EmployeeStockOwnershipPlanESOPCompensationExpense	8900000	USD
CY2011	us-gaap	Employee Stock Ownership Plan Esop Compensation Expense EmployeeStockOwnershipPlanESOPCompensationExpense	8800000	USD
CY2010Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice	18.80
CY2012Q2	nu	Share Based Compensation Arrangement By Share Based Payment Award Options Converted Nstar Options Upon Merger ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsConvertedNstarOptionsUponMerger	2664894	shares
CY2012Q2	nu	Share Based Compensation Arrangement By Share Based Payment Award Options Converted Nstar Options Upon Merger Total Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsConvertedNstarOptionsUponMergerTotalValue	30.5	USD
CY2012Q2	nu	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nstar Deferred And Performance Awards Converted Upon Merger ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNstarDeferredAndPerformanceAwardsConvertedUponMerger	421775	shares
CY2012Q2	nu	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nstar Deferred And Performance Awards Converted Upon Merger Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNstarDeferredAndPerformanceAwardsConvertedUponMergerValue	15.5	USD
CY2012Q2	nu	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nstar Rsu Retention Awards Converted To Nu Rsus Upon Merger ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNstarRsuRetentionAwardsConvertedToNuRsusUponMerger	195619	shares
CY2012Q2	nu	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nstar Rsu Retention Awards Converted To Nu Rsus Upon Merger Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNstarRsuRetentionAwardsConvertedToNuRsusUponMergerValue	7.2	USD
CY2013Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Authorized ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized	4500000	shares
CY2013Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Available For Grant ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant	2462668	shares
CY2012Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Available For Grant ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant	2502512	shares
CY2013Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Number ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	1162216	shares
CY2012Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Number ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	1417688	shares
CY2013Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue	36.58
CY2012Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue	34.70
CY2013	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod	583101	shares
CY2013	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue	34.34
CY2013	nu	Share Based Compensation Arrangement By Share Based Payment Award Vested Outstanding Number ShareBasedCompensationArrangementByShareBasedPaymentAwardVestedOutstandingNumber	474224	shares
CY2013	nu	Share Based Compensation Arrangement By Share Based Payment Award Expected To Vest ShareBasedCompensationArrangementByShareBasedPaymentAwardExpectedToVest	1104106	shares
CY2013	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	27000000	USD
CY2012	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	25800000	USD
CY2011	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	12300000	USD
CY2013	us-gaap	Employee Service Share Based Compensation Tax Benefit From Compensation Expense EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense	10700000	USD
CY2012	us-gaap	Employee Service Share Based Compensation Tax Benefit From Compensation Expense EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense	10200000	USD
CY2011	us-gaap	Employee Service Share Based Compensation Tax Benefit From Compensation Expense EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense	4900000	USD
CY2012	us-gaap	Excess Tax Benefit From Share Based Compensation Financing Activities ExcessTaxBenefitFromShareBasedCompensationFinancingActivities	8500000	USD
CY2011	us-gaap	Excess Tax Benefit From Share Based Compensation Financing Activities ExcessTaxBenefitFromShareBasedCompensationFinancingActivities	1300000	USD
CY2013	nu	Description Of Compensation Cost Not Yet Recognized Period For Recognition DescriptionOfCompensationCostNotYetRecognizedPeriodForRecognition	This cost is expected to be recognized ratably over a weighted-average period of 1.64 years for NU, 1.85 years for CL&P, 1.47 years for NSTAR Electric, 1.79 years for PSNH and 1.80 years for WMECO.
CY2013	us-gaap	Excess Tax Benefit From Share Based Compensation Financing Activities ExcessTaxBenefitFromShareBasedCompensationFinancingActivities	5500000	USD
CY2010Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber	112599	shares
CY2011	us-gaap	Stock Issued During Period Shares Stock Options Exercised StockIssuedDuringPeriodSharesStockOptionsExercised	-65225	shares
CY2011Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber	47374	shares
CY2013	us-gaap	Stock Issued During Period Shares Stock Options Exercised StockIssuedDuringPeriodSharesStockOptionsExercised	-324382	shares
CY2013Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber	1221375	shares
CY2011Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice	18.78
CY2013Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice	25.97
CY2011	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Exercises In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice	18.81
CY2013	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Exercises In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice	20.97
CY2011	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercises In Period Total Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue	1000000	USD
CY2013	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercises In Period Total Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue	6700000	USD
CY2013Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue	20100000	USD
CY2013Q4	us-gaap	Employee Service Share Based Compensation Nonvested Awards Total Compensation Cost Not Yet Recognized EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized	19500000	USD
CY2012Q2	nu	Share Based Compensation Arrangement By Share Based Payment Award Options Converted Nstar Options Upon Merger Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsConvertedNstarOptionsUponMergerWeightedAverageExercisePrice	23.99
CY2012	us-gaap	Stock Issued During Period Shares Stock Options Exercised StockIssuedDuringPeriodSharesStockOptionsExercised	-1166511	shares
CY2012	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Exercises In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice	22.53
CY2012	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercises In Period Total Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue	18700000	USD
CY2012Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber	1545757	shares
CY2012Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice	24.92
CY2013	us-gaap	Employee Service Share Based Compensation Cash Received From Exercise Of Stock Options EmployeeServiceShareBasedCompensationCashReceivedFromExerciseOfStockOptions	6800000	USD
CY2013	us-gaap	Employee Service Share Based Compensation Tax Benefit Realized From Exercise Of Stock Options EmployeeServiceShareBasedCompensationTaxBenefitRealizedFromExerciseOfStockOptions	2700000	USD
CY2013	us-gaap	Stock Issued During Period Shares Employee Stock Purchase Plans StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans	39526	shares
CY2012	us-gaap	Stock Issued During Period Shares Employee Stock Purchase Plans StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans	39422	shares
CY2013	nu	Espp Discounted Purchase Price First Six Months EsppDiscountedPurchasePriceFirstSixMonths	38.69	USD
CY2013	nu	Espp Discounted Purchase Price Second Six Months EsppDiscountedPurchasePriceSecondSixMonths	42.19	USD
CY2012	nu	Espp Discounted Purchase Price First Six Months EsppDiscountedPurchasePriceFirstSixMonths	33.01	USD
CY2012	nu	Espp Discounted Purchase Price Second Six Months EsppDiscountedPurchasePriceSecondSixMonths	37.89	USD
CY2013Q4	nu	Employee Stock Purchase Plan Shares Remaining For Future Issuance EmployeeStockPurchasePlanSharesRemainingForFutureIssuance	817754	shares
CY2012Q4	nu	Employee Stock Purchase Plan Shares Remaining For Future Issuance EmployeeStockPurchasePlanSharesRemainingForFutureIssuance	857280	shares
CY2013Q4	us-gaap	Deferred Compensation Cashbased Arrangements Liability Classified Noncurrent DeferredCompensationCashbasedArrangementsLiabilityClassifiedNoncurrent	51300000	USD
CY2012Q4	us-gaap	Deferred Compensation Cashbased Arrangements Liability Classified Noncurrent DeferredCompensationCashbasedArrangementsLiabilityClassifiedNoncurrent	54600000	USD
CY2011Q4	us-gaap	Deferred Compensation Cashbased Arrangements Liability Classified Noncurrent DeferredCompensationCashbasedArrangementsLiabilityClassifiedNoncurrent	52800000	USD
CY2013Q4	nu	Deferred Compensation Cash Based Arrangements Expense Pertaining To Deferred Benefits DeferredCompensationCashBasedArrangementsExpensePertainingToDeferredBenefits	4400000	USD
CY2012Q4	nu	Deferred Compensation Cash Based Arrangements Expense Pertaining To Deferred Benefits DeferredCompensationCashBasedArrangementsExpensePertainingToDeferredBenefits	4700000	USD
CY2011Q4	nu	Deferred Compensation Cash Based Arrangements Expense Pertaining To Deferred Benefits DeferredCompensationCashBasedArrangementsExpensePertainingToDeferredBenefits	4700000	USD
CY2013	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	8800000	USD
CY2012	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	-30900000	USD
CY2011	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	3000000	USD
CY2011	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	-26000000	USD
CY2012	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	17600000	USD
CY2013	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	-9400000	USD
CY2013	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	-600000	USD
CY2012	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	-13300000	USD
CY2011	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	-23000000	USD
CY2011	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	187700000	USD
CY2012	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	291300000	USD
CY2013	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	386200000	USD
CY2013	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	45400000	USD
CY2012	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	800000	USD
CY2011	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	9100000	USD
CY2011	us-gaap	Income Tax Reconciliation Tax Credits Investment IncomeTaxReconciliationTaxCreditsInvestment	-2800000	USD
CY2012	us-gaap	Income Tax Reconciliation Tax Credits Investment IncomeTaxReconciliationTaxCreditsInvestment	-3900000	USD
CY2013	us-gaap	Income Tax Reconciliation Tax Credits Investment IncomeTaxReconciliationTaxCreditsInvestment	-4100000	USD
CY2013	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	427200000	USD
CY2013	us-gaap	Income Tax Reconciliation Nondeductible Expense Depreciation IncomeTaxReconciliationNondeductibleExpenseDepreciation	-7400000	USD
CY2013	us-gaap	Income Tax Reconciliation Tax Credits Other IncomeTaxReconciliationTaxCreditsOther	-3700000	USD
CY2013	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	27600000	USD
CY2013	nu	Income Tax Reconciliation Medicare Subsidy IncomeTaxReconciliationMedicareSubsidy	-8000000	USD
CY2013	us-gaap	Income Tax Reconciliation Change In Deferred Tax Assets Valuation Allowance IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance	-4300000	USD
CY2013	us-gaap	Income Tax Reconciliation Other Adjustments IncomeTaxReconciliationOtherAdjustments	-400000	USD
CY2012	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	282800000	USD
CY2012	us-gaap	Income Tax Reconciliation Nondeductible Expense Depreciation IncomeTaxReconciliationNondeductibleExpenseDepreciation	-10800000	USD
CY2012	us-gaap	Income Tax Reconciliation Tax Credits Other IncomeTaxReconciliationTaxCreditsOther	-3800000	USD
CY2012	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	4400000	USD
CY2012	nu	Income Tax Reconciliation Medicare Subsidy IncomeTaxReconciliationMedicareSubsidy	-6400000	USD
CY2012	us-gaap	Income Tax Reconciliation Change In Deferred Tax Assets Valuation Allowance IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance	7600000	USD
CY2012	us-gaap	Income Tax Reconciliation Other Adjustments IncomeTaxReconciliationOtherAdjustments	5000000	USD
CY2011	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	200000000	USD
CY2011	us-gaap	Income Tax Reconciliation Nondeductible Expense Depreciation IncomeTaxReconciliationNondeductibleExpenseDepreciation	-14200000	USD
CY2011	us-gaap	Income Tax Reconciliation Tax Credits Other IncomeTaxReconciliationTaxCreditsOther	-3500000	USD
CY2011	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	22100000	USD
CY2011	nu	Income Tax Reconciliation Medicare Subsidy IncomeTaxReconciliationMedicareSubsidy	-2200000	USD
CY2011	us-gaap	Income Tax Reconciliation Change In Deferred Tax Assets Valuation Allowance IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance	-33100000	USD
CY2011	us-gaap	Income Tax Reconciliation Other Adjustments IncomeTaxReconciliationOtherAdjustments	4700000	USD
CY2013	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0.350	pure
CY2012	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0.340	pure
CY2011	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0.299	pure
CY2013Q4	us-gaap	Deferred Tax Assets Derivative Instruments DeferredTaxAssetsDerivativeInstruments	272900000	USD
CY2012Q4	us-gaap	Deferred Tax Assets Derivative Instruments DeferredTaxAssetsDerivativeInstruments	380600000	USD
CY2013Q4	us-gaap	Deferred Tax Assets Regulatory Assets And Liabilities DeferredTaxAssetsRegulatoryAssetsAndLiabilities	272700000	USD
CY2012Q4	us-gaap	Deferred Tax Assets Regulatory Assets And Liabilities DeferredTaxAssetsRegulatoryAssetsAndLiabilities	257900000	USD
CY2013Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefits	435200000	USD
CY2012Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefits	811400000	USD
CY2012Q4	nu	Deferred Tax Assets Tax Effect Tax Regulatory Assets DeferredTaxAssetsTaxEffectTaxRegulatoryAssets	17200000	USD
CY2013Q4	nu	Deferred Tax Assets Tax Effect Tax Regulatory Assets DeferredTaxAssetsTaxEffectTaxRegulatoryAssets	16200000	USD
CY2013Q4	us-gaap	Deferred Tax Assets Other DeferredTaxAssetsOther	230600000	USD
CY2012Q4	us-gaap	Deferred Tax Assets Other DeferredTaxAssetsOther	242400000	USD
CY2013Q4	us-gaap	Deferred Tax Assets Valuation Allowance DeferredTaxAssetsValuationAllowance	24300000	USD
CY2012Q4	us-gaap	Deferred Tax Assets Valuation Allowance DeferredTaxAssetsValuationAllowance	4200000	USD
CY2012Q4	us-gaap	Deferred Tax Assets Net DeferredTaxAssetsNet	2130500000	USD
CY2013Q4	us-gaap	Deferred Tax Assets Net DeferredTaxAssetsNet	1559100000	USD
CY2013Q4	us-gaap	Deferred Tax Liabilities Property Plant And Equipment DeferredTaxLiabilitiesPropertyPlantAndEquipment	3806500000	USD
CY2012Q4	nu	Deferred Tax Liabilities Regulatory Assets Securitized Contract Termination Costs DeferredTaxLiabilitiesRegulatoryAssetsSecuritizedContractTerminationCosts	16600000	USD
CY2013Q4	nu	Deferred Tax Liabilities Regulatory Assets Securitized Contract Termination Costs DeferredTaxLiabilitiesRegulatoryAssetsSecuritizedContractTerminationCosts	300000	USD
CY2013Q4	nu	Deferred Tax Liabilities Regulatory Assets Other Regulatory Deferrals DeferredTaxLiabilitiesRegulatoryAssetsOtherRegulatoryDeferrals	1146700000	USD
CY2012Q4	nu	Deferred Tax Liabilities Regulatory Assets Other Regulatory Deferrals DeferredTaxLiabilitiesRegulatoryAssetsOtherRegulatoryDeferrals	1561100000	USD
CY2012Q4	nu	Deferred Tax Liabilities Regulatory Assets Tax Effect Tax Regulatory Assets DeferredTaxLiabilitiesRegulatoryAssetsTaxEffectTaxRegulatoryAssets	217200000	USD
CY2013Q4	nu	Deferred Tax Liabilities Regulatory Assets Tax Effect Tax Regulatory Assets DeferredTaxLiabilitiesRegulatoryAssetsTaxEffectTaxRegulatoryAssets	248200000	USD
CY2013Q4	nu	Deferred Tax Liabilities Regulatory Assets Derivative Assets DeferredTaxLiabilitiesRegulatoryAssetsDerivativeAssets	30100000	USD
CY2012Q4	nu	Deferred Tax Liabilities Regulatory Assets Derivative Assets DeferredTaxLiabilitiesRegulatoryAssetsDerivativeAssets	36200000	USD
CY2012Q4	us-gaap	Deferred Tax Liabilities Other DeferredTaxLiabilitiesOther	136100000	USD
CY2013Q4	us-gaap	Deferred Tax Liabilities Other DeferredTaxLiabilitiesOther	156800000	USD
CY2013Q4	us-gaap	Deferred Tax Liabilities DeferredTaxLiabilities	5695200000	USD
CY2012Q4	us-gaap	Deferred Tax Liabilities DeferredTaxLiabilities	5736500000	USD
CY2013Q4	us-gaap	Deferred Tax Assets Gross DeferredTaxAssetsGross	1583400000	USD
CY2012Q4	us-gaap	Deferred Tax Assets Gross DeferredTaxAssetsGross	2134700000	USD
CY2013Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Allowance For Doubtful Accounts DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsAllowanceForDoubtfulAccounts	65000000	USD
CY2012Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Allowance For Doubtful Accounts DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsAllowanceForDoubtfulAccounts	64200000	USD
CY2013Q4	nu	Deferred Tax Liabilities Resulting From Property Tax Accruals And Other DeferredTaxLiabilitiesResultingFromPropertyTaxAccrualsAndOther	95100000	USD
CY2012Q4	nu	Deferred Tax Liabilities Resulting From Property Tax Accruals And Other DeferredTaxLiabilitiesResultingFromPropertyTaxAccrualsAndOther	89600000	USD
CY2012Q4	us-gaap	Deferred Tax Liabilities Property Plant And Equipment DeferredTaxLiabilitiesPropertyPlantAndEquipment	3468800000	USD
CY2013Q4	us-gaap	Deferred Tax Assets Operating Loss Carryforwards DeferredTaxAssetsOperatingLossCarryforwards	158000000	USD
CY2012Q4	us-gaap	Deferred Tax Assets Operating Loss Carryforwards DeferredTaxAssetsOperatingLossCarryforwards	214600000	USD
CY2013Q4	nu	Purchase Accounting Deferred Tax Asset PurchaseAccountingDeferredTaxAsset	132800000	USD
CY2012Q4	nu	Purchase Accounting Deferred Tax Asset PurchaseAccountingDeferredTaxAsset	146400000	USD
CY2013Q4	nu	Deferred Tax Liabilities Goodwill Regulatory Asset DeferredTaxLiabilitiesGoodwillRegulatoryAsset	211500000	USD
CY2012Q4	nu	Deferred Tax Liabilities Goodwill Regulatory Asset DeferredTaxLiabilitiesGoodwillRegulatoryAsset	210900000	USD
CY2010Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	101200000	USD
CY2011	us-gaap	Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions	8000000	USD
CY2011Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	73500000	USD
CY2012	us-gaap	Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions	10300000	USD
CY2012Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	83100000	USD
CY2012	us-gaap	Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions	100000	USD
CY2012	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions	-800000	USD
CY2011	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions	-35700000	USD
CY2013	us-gaap	Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions	8200000	USD
CY2013	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions	-1100000	USD
CY2013Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	38200000	USD
CY2013	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Settlements With Taxing Authorities UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities	-49800000	USD
CY2013	us-gaap	Unrecognized Tax Benefits Reductions Resulting From Lapse Of Applicable Statute Of Limitations UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations	-2200000	USD
CY2013	us-gaap	Unrecognized Tax Benefits Interest On Income Taxes Expense UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense	-8600000	USD
CY2012	us-gaap	Unrecognized Tax Benefits Interest On Income Taxes Expense UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense	3100000	USD
CY2011	us-gaap	Unrecognized Tax Benefits Interest On Income Taxes Expense UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense	-2800000	USD
CY2013Q4	us-gaap	Unrecognized Tax Benefits Interest On Income Taxes Accrued UnrecognizedTaxBenefitsInterestOnIncomeTaxesAccrued	1500000	USD
CY2012Q4	us-gaap	Unrecognized Tax Benefits Interest On Income Taxes Accrued UnrecognizedTaxBenefitsInterestOnIncomeTaxesAccrued	10100000	USD
CY2013	us-gaap	Income Tax Examination Description IncomeTaxExaminationDescription	Tax Positions: During 2013, NU received a Final Determination from the Connecticut Department of Revenue Services (DRS) that concluded its audit of NU's Connecticut income tax returns for the years 2005 through 2008. The DRS Determination resulted in total NU and CL&P after-tax benefits of $13.6 million and $6.9 million, respectively, that included a reduction in NU and CL&P pre-tax interest expense of $8.7 million and $4 million, or $5.2 million and $2.4 million after-tax, respectively. Further, the income tax expense impact resulted in a tax benefit to NU and CL&P of $8.4 million and $4.5 million after-tax, respectively. During 2011, NU recorded an after-tax benefit of $29.1 million related to various state tax settlements and certain other adjustments. This benefit was recorded as a reduction to both interest expense and income tax expense (including NU and CL&P tax expense reductions of approximately $22.4 million).
CY2011Q4	nu	Tax Adjustments Settlements Total Impact TaxAdjustmentsSettlementsTotalImpact	-29100000	USD
CY2011	us-gaap	Tax Adjustments Settlements And Unusual Provisions TaxAdjustmentsSettlementsAndUnusualProvisions	-22400000	USD
CY2013Q4	nu	Tax Adjustments Settlements Total Impact TaxAdjustmentsSettlementsTotalImpact	-13600000	USD
CY2013	us-gaap	Tax Adjustments Settlements And Unusual Provisions TaxAdjustmentsSettlementsAndUnusualProvisions	-8400000	USD
CY2011Q4	us-gaap	Accrual For Environmental Loss Contingencies AccrualForEnvironmentalLossContingencies	31700000	USD
CY2012	us-gaap	Accrual For Environmental Loss Contingencies Provision For New Losses AccrualForEnvironmentalLossContingenciesProvisionForNewLosses	4700000	USD
CY2012	us-gaap	Accrual For Environmental Loss Contingencies Payments AccrualForEnvironmentalLossContingenciesPayments	8800000	USD
CY2012Q4	us-gaap	Accrual For Environmental Loss Contingencies AccrualForEnvironmentalLossContingencies	39400000	USD
CY2013	us-gaap	Accrual For Environmental Loss Contingencies Provision For New Losses AccrualForEnvironmentalLossContingenciesProvisionForNewLosses	3500000	USD
CY2013	us-gaap	Accrual For Environmental Loss Contingencies Payments AccrualForEnvironmentalLossContingenciesPayments	7500000	USD
CY2013Q4	us-gaap	Accrual For Environmental Loss Contingencies AccrualForEnvironmentalLossContingencies	35400000	USD
CY2012	nu	Environmental Liability Assumed In Merger EnvironmentalLiabilityAssumedInMerger	11800000	USD
CY2013	nu	Environmental Site Quantity EnvironmentalSiteQuantity	68	pure
CY2012	nu	Environmental Site Quantity EnvironmentalSiteQuantity	77	pure
CY2013Q4	nu	Superfund Site Information SuperfundSiteInformation	CERCLA: The federal Comprehensive Environmental Response, Compensation and Liability Act of 1980 (CERCLA) and its amendments or state equivalents impose joint and several strict liabilities, regardless of fault, upon generators of hazardous substances resulting in removal and remediation costs and environmental damages.  Liabilities under these laws can be material and in some instances may be imposed without regard to fault or for past acts that may have been lawful at the time they occurred.  Of the 68 sites, 10 sites (2 for CL&P, 3 for NSTAR Electric, 4 for PSNH and 1 for WMECO) are superfund sites under CERCLA for which the Company has been notified that it is a potentially responsible party but for which the site assessment and remediation are not being managed by the Company.  As of December 31, 2013, a liability of $1 million ($0.4 million for CL&P, and $0.3 million for PSNH) accrued on these sites represents management's best estimate of its potential remediation costs with respect to these superfund sites.
CY2013Q4	nu	Range Of Potential Loss On Enivornmental Sites RangeOfPotentialLossOnEnivornmentalSites	As of December 31, 2013, for 6 environmental sites (2 for PSNH, and 1 for WMECO) that are included in the Company's reserve for environmental costs, the information known and nature of the remediation options at those sites allow for the Company to estimate the range of losses for environmental costs. As of December 31, 2013, $5.8 million ($0.7 million for PSNH) had been accrued as a liability for these sites, which represent management's best estimates of the liabilities for environmental costs. These amounts are the best estimates with estimated ranges of additional losses from zero to $30 million (zero to $4.2 million for PSNH, and zero to $8.6 million for WMECO). As of December 31, 2013, for 20 environmental sites (4 for CL&P, 1 for NSTAR Electric, 3 for PSNH, and 2 for WMECO) that are included in the Company’s reserve for environmental costs, management cannot reasonably estimate the exposure to loss in excess of the reserve, or range of loss, as these sites are under investigation and/or there is significant uncertainty as to what remedial actions, if any, the Company may be required to undertake. As of December 31, 2013, $16.7 million ($1.6 million for CL&P, $0.1 million for PSNH, and $0.3 million for WMECO) had been accrued as a liability for these sites. As of December 31, 2013, for the remaining 42 environmental sites (14 for CL&P, 11 for NSTAR Electric, 10 for PSNH, and 2 for WMECO) that are included in the Company’s reserve for environmental costs, the $12.9 million accrual ($1.8 million for CL&P, $1.2 million for NSTAR Electric, $4.6 million for PSNH, and $0.1 million for WMECO) represents management’s best estimate of the liability and no additional loss is anticipated.
CY2013Q4	us-gaap	Unrecorded Unconditional Purchase Obligation Balance On Third Anniversary UnrecordedUnconditionalPurchaseObligationBalanceOnThirdAnniversary	538100000	USD
CY2013Q4	us-gaap	Unrecorded Unconditional Purchase Obligation Balance On Fourth Anniversary UnrecordedUnconditionalPurchaseObligationBalanceOnFourthAnniversary	428700000	USD
CY2013Q4	us-gaap	Unrecorded Unconditional Purchase Obligation Balance On Fifth Anniversary UnrecordedUnconditionalPurchaseObligationBalanceOnFifthAnniversary	368100000	USD
CY2013Q4	us-gaap	Unrecorded Unconditional Purchase Obligation Due After Five Years UnrecordedUnconditionalPurchaseObligationDueAfterFiveYears	2385600000	USD
CY2013Q4	us-gaap	Unrecorded Unconditional Purchase Obligation Balance Sheet Amount UnrecordedUnconditionalPurchaseObligationBalanceSheetAmount	5041500000	USD
CY2013Q4	us-gaap	Unrecorded Unconditional Purchase Obligation Balance On First Anniversary UnrecordedUnconditionalPurchaseObligationBalanceOnFirstAnniversary	705400000	USD
CY2013Q4	us-gaap	Unrecorded Unconditional Purchase Obligation Balance On Second Anniversary UnrecordedUnconditionalPurchaseObligationBalanceOnSecondAnniversary	615600000	USD
CY2012	nu	Supply And Stranded Costs Obligations Incurred SupplyAndStrandedCostsObligationsIncurred	216800000	USD
CY2011	nu	Supply And Stranded Costs Obligations Incurred SupplyAndStrandedCostsObligationsIncurred	156000000	USD
CY2012	nu	Peaker Cfd Expense Incurred PeakerCfdExpenseIncurred	59300000	USD
CY2011	nu	Peaker Cfd Expense Incurred PeakerCfdExpenseIncurred	40200000	USD
CY2012	nu	Natural Gas Procurement Costs Incurred NaturalGasProcurementCostsIncurred	243100000	USD
CY2011	nu	Natural Gas Procurement Costs Incurred NaturalGasProcurementCostsIncurred	191700000	USD
CY2012	nu	Fuel Costs Incurred FuelCostsIncurred	105200000	USD
CY2013	nu	Fuel Costs Incurred FuelCostsIncurred	112600000	USD
CY2012	nu	Transmission Support Commitment Costs Incurred TransmissionSupportCommitmentCostsIncurred	24800000	USD
CY2011	nu	Transmission Support Commitment Costs Incurred TransmissionSupportCommitmentCostsIncurred	18100000	USD
CY2012	nu	Renewable Energy Costs Incurred RenewableEnergyCostsIncurred	48700000	USD
CY2011	nu	Renewable Energy Costs Incurred RenewableEnergyCostsIncurred	5100000	USD
CY2012Q4	nu	Court Of Federal Claims Ruling To Cyapc CourtOfFederalClaimsRulingToCyapc	39600000	USD
CY2012Q4	nu	Court Of Federal Claims Ruling To Yaec CourtOfFederalClaimsRulingToYaec	38300000	USD
CY2012Q4	nu	Court Of Federal Claims Ruling To Myapc CourtOfFederalClaimsRulingToMyapc	81700000	USD
CY2013Q4	nu	Increase In Marketable Securities Current Period IncreaseInMarketableSecuritiesCurrentPeriod	77900000	USD
CY2013Q4	nu	Court Of Federal Claims Ruling To Cyapc CourtOfFederalClaimsRulingToCyapc	126300000	USD
CY2013Q4	nu	Court Of Federal Claims Ruling To Yaec CourtOfFederalClaimsRulingToYaec	73300000	USD
CY2013Q4	nu	Court Of Federal Claims Ruling To Myapc CourtOfFederalClaimsRulingToMyapc	35800000	USD
CY2013	us-gaap	Loss Contingency Managements Assessment And Process LossContingencyManagementsAssessmentAndProcess	E.         FERC Base ROE Complaint On September 30, 2011, several New England state attorneys general, state regulatory commissions, consumer advocates and other parties filed a joint complaint with the FERC under Sections 206 and 306 of the Federal Power Act alleging that the base ROE used in calculating formula rates for transmission service under the ISO-NE Open Access Transmission Tariff by NETOs, including CL&P, NSTAR Electric, PSNH and WMECO, is unjust and unreasonable. The complainants asserted that the current 11.14 percent rate, which became effective in 2006, is excessive due to changes in the capital markets and are seeking an order to reduce the rate, which would be effective October 1, 2011. In response, the NETOs filed testimony and analysis based on standard FERC methodology and precedent demonstrating that the base ROE of 11.14 percent remained just and reasonable. The FERC set the case for trial before a FERC ALJ after settlement negotiations were unsuccessful in August 2012. Hearings before the FERC ALJ were held in May 2013, followed by the filing of briefs by the complainants, the Massachusetts municipal electric utilities (late interveners to the case), the FERC trial staff and the NETOs. The NETOs recommended that the current base ROE of 11.14 percent should remain in effect for the refund period (October 1, 2011 through December 31, 2012) and the prospective period (beginning when FERC issues its final decision). The complainants, the Massachusetts municipal electric utilities, and the FERC trial staff each recommended a base ROE of 9 percent or below. On August 6, 2013, the FERC ALJ issued an initial decision, finding that the base ROE in effect from October 2011 through December 2012 was not reasonable under the standard application of FERC methodology, but leaving policy considerations and additional adjustments to the FERC. Using the established FERC methodology, the FERC ALJ determined that separate base ROEs should be set for the refund period and the prospective period. The FERC ALJ found those base ROEs to be 10.6 percent and 9.7 percent, respectively. The FERC may adjust the prospective period base ROE in its final decision to reflect movement in 10-year Treasury bond rates from the date that the case was filed (April 2013) to the date of the final decision. The parties filed briefs on this decision with the FERC, and a decision from the FERC is expected in 2014. Though NU cannot predict the ultimate outcome of this proceeding, in 2013 the Company recorded a series of reserves at its electric subsidiaries to recognize the potential financial impact from the FERC ALJ's initial decision for the refund period. The aggregate after-tax charge to earnings totaled $14.3 million at NU, which represents reserves of $7.7 million at CL&P, $3.4 million at NSTAR Electric, $1.4 million at PSNH and $1.8 million at WMECO. On December 27, 2012, several additional parties filed a separate complaint concerning the NETOs' base ROE with the FERC. This complaint seeks to reduce the NETOs’ base ROE effective January 1, 2013, effectively extending the refund period for an additional 15 months, and to consolidate this complaint with the joint complaint filed on September 30, 2011. The NETOs have asked the FERC to reject this complaint. The FERC has not yet acted on this complaint, and management is unable to predict the ultimate outcome or estimate the impacts of this complaint on financial position, results of operations or cash flows. As of December 31, 2013, the CL&P, NSTAR Electric, PSNH, and WMECO aggregate shareholder equity invested in their transmission facilities was approximately $2.3 billion. As a result, each 10 basis point change in the prospective period authorized base ROE would change annual consolidated earnings by an approximate $2.3 million. F.        DPU Safety and Reliability Programs - CPSL Since 2006, NSTAR Electric has been recovering incremental costs related to the DPU-approved Safety and Reliability Programs. From 2006 through 2011, cumulative costs associated with the CPSL program resulted in an incremental revenue requirement to customers of approximately $83 million. These amounts included incremental operations and maintenance costs and the related revenue requirement for specific capital investments relative to the CPSL programs. On May 28, 2010, the DPU issued an order on NSTAR Electric’s 2006 CPSL cost recovery filing (the May 2010 Order). In October 2010, NSTAR Electric filed a reconciliation of the cumulative CPSL program activity for the periods 2006 through 2009 with the DPU in order to determine a proposed rate adjustment. The DPU allowed the proposed rates to go into effect January 1, 2011, subject to final reconciliation of CPSL program costs through a future DPU proceeding. In February 2013, NSTAR Electric updated the October 2010 filing with final activity through 2011. NSTAR Electric recorded its 2006 through 2011 revenues under the CPSL programs based on the May 2010 Order. NSTAR Electric cannot predict the timing of a final DPU order related to its CPSL filings for the period 2006 through 2011. While management does not believe that any subsequent DPU order would result in revenues that are materially different than the amounts already recognized, it is reasonably possible that an order could have a material impact on NSTAR Electric’s results of operations, financial position and cash flows. The April 4, 2012 DPU-approved comprehensive merger settlement agreement with the Massachusetts Attorney General stipulates that NSTAR Electric must incur a revenue requirement of at least $15 million per year for 2012 through 2015 related to these programs. CPSL revenues will end once NSTAR Electric has recovered its 2015-related CPSL costs. Realization of these revenues is subject to maintaining certain performance metrics over the four-year period and DPU approval. As of December 31, 2013, NSTAR Electric was in compliance with the performance metrics and has recognized the entire $15 million revenue requirement during 2013 and 2012. G.        Basic Service Bad Debt Adder In accordance with a generic DPU order, electric utilities in Massachusetts recover the energy-related portion of bad debt costs in their Basic Service rates. In 2007, NSTAR Electric filed its 2006 Basic Service reconciliation with the DPU proposing an adjustment related to the increase of its Basic Service bad debt charge-offs. The DPU issued an order approving the implementation of a revised Basic Service rate but instructed NSTAR Electric to reduce distribution rates by an amount equal to the increase in its Basic Service bad debt charge-offs. This adjustment to NSTAR Electric’s distribution rates would eliminate the fully reconciling nature of the Basic Service bad debt adder. In 2010, NSTAR Electric filed an appeal of the DPU’s order with the SJC. In 2012, the SJC vacated the DPU order and remanded the matter to the DPU for further review. The DPU has not taken any action on the remand. NSTAR Electric deferred approximately $34 million of costs associated with energy-related bad debt as a regulatory asset through 2011 as NSTAR Electric had concluded that it was probable that these costs would ultimately be recovered from customers. Due to the delays and the duration of the proceedings, NSTAR Electric concluded that while an ultimate outcome on the matter in its favor remained "more likely than not," it could no longer be deemed "probable." As a result, NSTAR Electric recognized a reserve related to the regulatory asset in 2012. NSTAR Electric will continue to maintain the reserve until the proceeding has been concluded with the DPU.
CY2013	us-gaap	Lease And Rental Expense LeaseAndRentalExpense	16300000	USD
CY2012	us-gaap	Lease And Rental Expense LeaseAndRentalExpense	14800000	USD
CY2011	us-gaap	Lease And Rental Expense LeaseAndRentalExpense	8400000	USD
CY2013Q4	us-gaap	Capital Leases Future Minimum Payments Due Current CapitalLeasesFutureMinimumPaymentsDueCurrent	2600000	USD
CY2013Q4	us-gaap	Capital Leases Future Minimum Payments Due In Two Years CapitalLeasesFutureMinimumPaymentsDueInTwoYears	2400000	USD
CY2013Q4	us-gaap	Capital Leases Future Minimum Payments Due In Three Years CapitalLeasesFutureMinimumPaymentsDueInThreeYears	2200000	USD
CY2013Q4	us-gaap	Capital Leases Future Minimum Payments Due In Four Years CapitalLeasesFutureMinimumPaymentsDueInFourYears	2100000	USD
CY2013Q4	us-gaap	Capital Leases Future Minimum Payments Due In Five Years CapitalLeasesFutureMinimumPaymentsDueInFiveYears	2100000	USD
CY2013Q4	us-gaap	Capital Leases Future Minimum Payments Due Thereafter CapitalLeasesFutureMinimumPaymentsDueThereafter	5400000	USD
CY2013Q4	us-gaap	Capital Leases Future Minimum Payments Due CapitalLeasesFutureMinimumPaymentsDue	16800000	USD
CY2013Q4	us-gaap	Capital Leases Future Minimum Payments Interest Included In Payments CapitalLeasesFutureMinimumPaymentsInterestIncludedInPayments	6100000	USD
CY2013Q4	us-gaap	Capital Leases Future Minimum Payments Present Value Of Net Minimum Payments CapitalLeasesFutureMinimumPaymentsPresentValueOfNetMinimumPayments	10700000	USD
CY2013Q4	us-gaap	Operating Leases Future Minimum Payments Due OperatingLeasesFutureMinimumPaymentsDue	96800000	USD
CY2013	us-gaap	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Prior Service Cost Credit Before Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax	-200000	USD
CY2013	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax	4300000	USD
CY2012	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci On Derivatives Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesBeforeTax	-3300000	USD
CY2011	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci On Derivatives Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesBeforeTax	-1300000	USD
CY2013Q4	us-gaap	Operating Leases Future Minimum Payments Due Current OperatingLeasesFutureMinimumPaymentsDueCurrent	20100000	USD
CY2013Q4	us-gaap	Operating Leases Future Minimum Payments Due In Two Years OperatingLeasesFutureMinimumPaymentsDueInTwoYears	18100000	USD
CY2013Q4	us-gaap	Operating Leases Future Minimum Payments Due In Three Years OperatingLeasesFutureMinimumPaymentsDueInThreeYears	15400000	USD
CY2013Q4	us-gaap	Operating Leases Future Minimum Payments Due In Four Years OperatingLeasesFutureMinimumPaymentsDueInFourYears	12400000	USD
CY2013Q4	us-gaap	Operating Leases Future Minimum Payments Due In Five Years OperatingLeasesFutureMinimumPaymentsDueInFiveYears	8500000	USD
CY2013Q4	us-gaap	Operating Leases Future Minimum Payments Due Thereafter OperatingLeasesFutureMinimumPaymentsDueThereafter	22300000	USD
CY2012Q4	us-gaap	Accumulated Other Comprehensive Income Loss Cumulative Changes In Net Gain Loss From Cash Flow Hedges Effect Net Of Tax AccumulatedOtherComprehensiveIncomeLossCumulativeChangesInNetGainLossFromCashFlowHedgesEffectNetOfTax	-16400000	USD
CY2013	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci On Derivatives Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesNetOfTax	2000000	USD
CY2013Q4	us-gaap	Accumulated Other Comprehensive Income Loss Cumulative Changes In Net Gain Loss From Cash Flow Hedges Effect Net Of Tax AccumulatedOtherComprehensiveIncomeLossCumulativeChangesInNetGainLossFromCashFlowHedgesEffectNetOfTax	-14400000	USD
CY2012Q4	us-gaap	Accumulated Other Comprehensive Income Loss Available For Sale Securities Adjustment Net Of Tax AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax	1300000	USD
CY2013	us-gaap	Other Comprehensive Income Loss Available For Sale Securities Adjustment Before Reclassification Adjustments Net Of Tax OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeReclassificationAdjustmentsNetOfTax	900000	USD
CY2013Q4	us-gaap	Accumulated Other Comprehensive Income Loss Available For Sale Securities Adjustment Net Of Tax AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax	400000	USD
CY2012Q4	us-gaap	Accumulated Other Comprehensive Income Loss Defined Benefit Pension And Other Postretirement Plans Net Of Tax AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax	57800000	USD
CY2013	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansNetOfTax	6400000	USD
CY2013Q4	us-gaap	Accumulated Other Comprehensive Income Loss Defined Benefit Pension And Other Postretirement Plans Net Of Tax AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax	32000000	USD
CY2013	nu	Othercomprehensiveincomebeforereclassifications Othercomprehensiveincomebeforereclassifications	18500000	USD
CY2013	nu	Amountreclassifiedfromaoci Amountreclassifiedfromaoci	8400000	USD
CY2013Q4	us-gaap	Defined Benefit Plan Accumulated Other Comprehensive Income Net Gains Losses After Tax DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesAfterTax	19400000	USD
CY2013	us-gaap	Other Comprehensive Income Defined Benefit Plans Net Unamortized Gain Loss Arising During Period Tax OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodTax	-11400000	USD
CY2012	us-gaap	Other Comprehensive Income Defined Benefit Plans Net Unamortized Gain Loss Arising During Period Tax OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodTax	6200000	USD
CY2011	us-gaap	Other Comprehensive Income Defined Benefit Plans Net Unamortized Gain Loss Arising During Period Tax OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodTax	10200000	USD
CY2011	us-gaap	Other Comprehensive Income Unrealized Gain Loss On Derivatives Arising During Period Tax OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodTax	10200000	USD
CY2013	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci On Derivatives Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesBeforeTax	-3400000	USD
CY2013	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci On Derivatives Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesTax	1400000	USD
CY2013	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansBeforeTax	-10500000	USD
CY2012	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci On Derivatives Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesTax	1300000	USD
CY2011	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci On Derivatives Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesTax	600000	USD
CY2011	us-gaap	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Prior Service Cost Credit Before Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax	-300000	USD
CY2012	us-gaap	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Prior Service Cost Credit Before Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax	-200000	USD
CY2012	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansBeforeTax	-8900000	USD
CY2011	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansBeforeTax	-5700000	USD
CY2012	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax	3500000	USD
CY2011	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax	2300000	USD
CY2013	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax	-10700000	USD
CY2012	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax	-9300000	USD
CY2011	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax	-6200000	USD
CY2012	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci On Derivatives Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesNetOfTax	2000000	USD
CY2011	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci On Derivatives Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesNetOfTax	700000	USD
CY2012	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Transition Asset Obligation Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax	-200000	USD
CY2011	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Transition Asset Obligation Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax	-200000	USD
CY2011	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansNetOfTax	3900000	USD
CY2012	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansNetOfTax	5800000	USD
CY2012	nu	Amountreclassifiedfromaoci Amountreclassifiedfromaoci	7800000	USD
CY2011	nu	Amountreclassifiedfromaoci Amountreclassifiedfromaoci	4600000	USD
CY2013	us-gaap	Cash Flow Hedge Gain Loss To Be Reclassified Within Twelve Months CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths	3400000	USD
CY2013	nu	Pension Serp And Pbop Gain Loss To Be Reclassified Within Twelve Months PensionSerpAndPbopGainLossToBeReclassifiedWithinTwelveMonths	6500000	USD
CY2013	us-gaap	Line Of Credit Facility Dividend Restrictions LineOfCreditFacilityDividendRestrictions	CL&P, NSTAR Electric, PSNH and WMECO are subject to Section 305 of the Federal Power Act that makes it unlawful for a public utility to make or pay a dividend from any funds "properly included in its capital account." Management believes that this Federal Power Act restriction, as applied to CL&P, NSTAR Electric, PSNH and WMECO, would not be construed or applied by the FERC to prohibit the payment of dividends for lawful and legitimate business purposes from retained earnings. In addition, certain state statutes may impose additional limitations on such companies and on Yankee Gas and NSTAR Gas. Such state law restrictions do not restrict payment of dividends from retained earnings or net income. Pursuant to the joint revolving credit agreement of NU, CL&P, PSNH, WMECO, Yankee Gas and NSTAR Gas, and the NSTAR Electric revolving credit agreement, each company is required to maintain consolidated total debt to total capitalization ratio of no greater than 65 percent at all times. As of December 31, 2013, all companies were in compliance with such covenant. The Retained Earnings balances subject to these restrictions were $2.1 billion for NU, $961.5 million for CL&P, $1.4 billion for NSTAR Electric, $438.5 million for PSNH and $181 million for WMECO as of December 31, 2013.
CY2013Q4	us-gaap	Common Stock Par Or Stated Value Per Share CommonStockParOrStatedValuePerShare	5
CY2012Q4	us-gaap	Common Stock Shares Issued CommonStockSharesIssued	332509383	shares
CY2013Q4	us-gaap	Common Stock Shares Issued CommonStockSharesIssued	333113492	shares
CY2012Q4	us-gaap	Common Stock Shares Authorized CommonStockSharesAuthorized	380000000	shares
CY2013Q4	us-gaap	Common Stock Shares Authorized CommonStockSharesAuthorized	380000000	shares
CY2013Q4	us-gaap	Treasury Stock Shares TreasuryStockShares	17796672	shares
CY2012Q4	us-gaap	Treasury Stock Shares TreasuryStockShares	18455749	shares
CY2012Q4	us-gaap	Common Stock Par Or Stated Value Per Share CommonStockParOrStatedValuePerShare	5
CY2013Q4	us-gaap	Preferred Stock Value Outstanding PreferredStockValueOutstanding	155600000	USD
CY2012Q4	us-gaap	Preferred Stock Value Outstanding PreferredStockValueOutstanding	155600000	USD
CY2011	nu	Other Impacts Of Merger With Nstar OtherImpactsOfMergerWithNstar	39400000	USD
CY2013	us-gaap	Weighted Average Number Diluted Shares Outstanding Adjustment WeightedAverageNumberDilutedSharesOutstandingAdjustment	899773	shares
CY2012	us-gaap	Weighted Average Number Diluted Shares Outstanding Adjustment WeightedAverageNumberDilutedSharesOutstandingAdjustment	783812	shares
CY2011	us-gaap	Weighted Average Number Diluted Shares Outstanding Adjustment WeightedAverageNumberDilutedSharesOutstandingAdjustment	394401	shares
CY2013	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	2.49
CY2012	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	1.90
CY2011	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	2.22
CY2013	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	2.49
CY2012	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	1.89
CY2011	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	2.22
CY2013	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	315311387	shares
CY2013	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	316211160	shares
CY2012	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	277209819	shares
CY2012	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	277993631	shares
CY2011	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	177410167	shares
CY2011	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	177804568	shares
CY2013	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	1575	shares
CY2012	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	4266	shares
CY2011	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	4314	shares
CY2013	us-gaap	Subsequent Event Description SubsequentEventDescription	See Note 9, "Long-Term Debt," for information regarding the January 2014 Yankee Gas long-term debt issuance. See Note 3, "Regulatory Accounting," for information regarding the February 2014 PURA decision on CL&P’s request for approval to recover the restoration costs of the 2012 and 2011 major storms. See Note 12C, "Commitments and Contingencies - Contractual Obligations - Yankee Companies," for information regarding a January 2014 letter received from the U.S. Department of Justice stating that the DOE will not appeal the court's final judgment on the Yankee Companies' lawsuits against the DOE.
CY2013Q2	us-gaap	Revenues Revenues	1635900000	USD
CY2013Q3	us-gaap	Revenues Revenues	1892600000	USD
CY2013Q3	us-gaap	Operating Income Loss OperatingIncomeLoss	399300000	USD
CY2013Q2	us-gaap	Operating Income Loss OperatingIncomeLoss	350600000	USD
CY2013Q2	us-gaap	Net Income Loss NetIncomeLoss	173100000	USD
CY2013Q3	us-gaap	Net Income Loss NetIncomeLoss	211400000	USD
CY2013Q3	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	209500000	USD
CY2013Q2	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	171000000	USD
CY2013Q1	us-gaap	Revenues Revenues	1995000000	USD
CY2013Q1	us-gaap	Operating Income Loss OperatingIncomeLoss	418900000	USD
CY2013Q1	us-gaap	Net Income Loss NetIncomeLoss	230000000	USD
CY2012Q1	us-gaap	Revenues Revenues	1099600000	USD
CY2012Q1	us-gaap	Operating Income Loss OperatingIncomeLoss	214400000	USD
CY2012Q1	us-gaap	Net Income Loss NetIncomeLoss	100800000	USD
CY2012Q1	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	99300000	USD
CY2013Q1	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	228100000	USD
CY2013Q4	us-gaap	Revenues Revenues	1777700000	USD
CY2013Q4	us-gaap	Operating Income Loss OperatingIncomeLoss	360600000	USD
CY2013Q4	us-gaap	Net Income Loss NetIncomeLoss	179200000	USD
CY2013Q4	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	177400000	USD
CY2012Q4	us-gaap	Revenues Revenues	1684000000	USD
CY2012Q4	us-gaap	Operating Income Loss OperatingIncomeLoss	331400000	USD
CY2012Q4	us-gaap	Net Income Loss NetIncomeLoss	176600000	USD
CY2012Q4	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	174700000	USD
CY2013Q1	us-gaap	Earnings Per Share Basic And Diluted EarningsPerShareBasicAndDiluted	0.72
CY2013Q2	us-gaap	Earnings Per Share Basic And Diluted EarningsPerShareBasicAndDiluted	0.54
CY2013Q3	us-gaap	Earnings Per Share Basic And Diluted EarningsPerShareBasicAndDiluted	0.66
CY2013Q4	us-gaap	Earnings Per Share Basic And Diluted EarningsPerShareBasicAndDiluted	0.56
CY2012Q4	us-gaap	Earnings Per Share Basic And Diluted EarningsPerShareBasicAndDiluted	0.55
CY2012Q3	us-gaap	Earnings Per Share Basic And Diluted EarningsPerShareBasicAndDiluted	0.66
CY2012Q2	us-gaap	Earnings Per Share Basic And Diluted EarningsPerShareBasicAndDiluted	0.15
CY2012Q1	us-gaap	Earnings Per Share Basic And Diluted EarningsPerShareBasicAndDiluted	0.56
CY2013	us-gaap	Valuation Allowances And Reserves Charged To Cost And Expense ValuationAllowancesAndReservesChargedToCostAndExpense	55465000	USD
CY2012	us-gaap	Valuation Allowances And Reserves Charged To Cost And Expense ValuationAllowancesAndReservesChargedToCostAndExpense	36275000	USD
CY2011	us-gaap	Valuation Allowances And Reserves Charged To Cost And Expense ValuationAllowancesAndReservesChargedToCostAndExpense	16420000	USD
CY2013	us-gaap	Valuation Allowances And Reserves Deductions ValuationAllowancesAndReservesDeductions	87507000	USD
CY2012	us-gaap	Valuation Allowances And Reserves Deductions ValuationAllowancesAndReservesDeductions	80462000	USD
CY2011	us-gaap	Valuation Allowances And Reserves Deductions ValuationAllowancesAndReservesDeductions	60584000	USD
CY2010Q4	us-gaap	Valuation Allowances And Reserves Balance ValuationAllowancesAndReservesBalance	119190000	USD
CY2011Q4	us-gaap	Valuation Allowances And Reserves Balance ValuationAllowancesAndReservesBalance	115689000	USD
CY2012Q4	us-gaap	Valuation Allowances And Reserves Balance ValuationAllowancesAndReservesBalance	165549000	USD
CY2013Q4	us-gaap	Valuation Allowances And Reserves Balance ValuationAllowancesAndReservesBalance	171251000	USD
CY2013	us-gaap	Valuation Allowances And Reserves Charged To Other Accounts ValuationAllowancesAndReservesChargedToOtherAccounts	37744000	USD
CY2012	us-gaap	Valuation Allowances And Reserves Charged To Other Accounts ValuationAllowancesAndReservesChargedToOtherAccounts	34761000	USD
CY2011	us-gaap	Valuation Allowances And Reserves Charged To Other Accounts ValuationAllowancesAndReservesChargedToOtherAccounts	40663000	USD
CY2013Q4	nu	Impact Related To Nstar Merger ImpactRelatedToNstarMerger	0	USD
CY2012Q4	nu	Uncollectible Hardship Accounts Receivable Reserves UncollectibleHardshipAccountsReceivableReserves	68600000	USD
CY2011Q4	nu	Uncollectible Hardship Accounts Receivable Reserves UncollectibleHardshipAccountsReceivableReserves		USD
CY2012Q4	nu	Impact Related To Nstar Merger ImpactRelatedToNstarMerger	59286000	USD
CY2013	dei	Entity Registrant Name EntityRegistrantName	NORTHEAST UTILITIES
CY2013	dei	Document Type DocumentType	10-K
CY2013	dei	Document Period End Date DocumentPeriodEndDate	2013-12-31
CY2013	dei	Entity Central Index Key EntityCentralIndexKey	0000072741
CY2013	dei	Current Fiscal Year End Date CurrentFiscalYearEndDate	--12-31
CY2014Q1	dei	Entity Common Stock Shares Outstanding EntityCommonStockSharesOutstanding	315434940	shares
CY2013Q2	dei	Entity Public Float EntityPublicFloat	13224337788	USD
CY2013	dei	Entity Filer Category EntityFilerCategory	Large Accelerated Filer
CY2013	dei	Entity Current Reporting Status EntityCurrentReportingStatus	Yes
CY2013	dei	Entity Voluntary Filers EntityVoluntaryFilers	No
CY2013	dei	Entity Well Known Seasoned Issuer EntityWellKnownSeasonedIssuer	Yes
CY2013	dei	Document Fiscal Year Focus DocumentFiscalYearFocus	2013
CY2013	dei	Document Fiscal Period Focus DocumentFiscalPeriodFocus	FY
CY2013	dei	Amendment Flag AmendmentFlag	false
CY2012Q4	us-gaap	Other Assets Current OtherAssetsCurrent	199947000	USD
CY2012Q4	us-gaap	Accounts Receivable Net Current AccountsReceivableNetCurrent	792822000	USD
CY2013Q4	us-gaap	Other Assets Current OtherAssetsCurrent	214288000	USD
CY2012Q4	us-gaap	Costs In Excess Of Billings On Uncompleted Contracts Or Programs Expected To Be Collected Within One Year CostsInExcessOfBillingsOnUncompletedContractsOrProgramsExpectedToBeCollectedWithinOneYear	216040000	USD
CY2012Q4	us-gaap	Regulatory Assets Noncurrent RegulatoryAssetsNoncurrent	5132411000	USD
CY2013Q4	us-gaap	Marketable Securities Noncurrent MarketableSecuritiesNoncurrent	488515000	USD
CY2013	us-gaap	Proceeds From Payments For Other Financing Activities ProceedsFromPaymentsForOtherFinancingActivities	-25253000	USD
CY2013	us-gaap	Cash And Cash Equivalents Period Increase Decrease CashAndCashEquivalentsPeriodIncreaseDecrease	-2384000	USD
CY2013Q4	us-gaap	Assets Current AssetsCurrent	2087049000	USD

Files In Submission

Name	View Source	Status
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0000072741-14-000011-index.html	Edgar Link	pending
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$ES
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2013 Q4 Form 10-K Financial Statement

#000007274114000011 Filed on February 25, 2014

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$ES EVERSOURCE ENERGY Stock $es

2013 Q4 Form 10-K Financial Statement

#000007274114000011 Filed on February 25, 2014

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$ES
EVERSOURCE ENERGY Stock $es