$MMC
MARSH & MCLENNAN COMPANIES, INC. Stock $mmc

$mmc Overview Financials Valuation SEC Filings Company Website

2020 Q4 Form 10-K Financial Statement

#000006270921000008 Filed on February 17, 2021

Income Statement

Concept	2020 Q4	2019 Q4	2019 Q3
Revenue	$4.416B	$4.264B	$3.968B
YoY Change	3.56%	14.87%	13.24%
Cost Of Revenue
YoY Change
Gross Profit
YoY Change
Gross Profit Margin
Selling, General & Admin	$2.650B	$2.478B	$2.437B
YoY Change	6.94%	14.56%	16.99%
% of Gross Profit
Research & Development
YoY Change
% of Gross Profit
Depreciation & Amortization	$194.0M	$167.0M	$170.0M
YoY Change	16.17%	35.77%	37.1%
% of Gross Profit
Operating Expenses	$3.775B	$3.529B	$3.501B
YoY Change	6.97%	14.17%	18.16%
Operating Profit	$571.0M	$592.0M	$467.0M
YoY Change	-3.55%	-4.67%	-13.68%
Interest Expense	-$101.0M	-$123.0M	$133.0M
YoY Change	-17.89%	-70.57%	92.75%
% of Operating Profit	-17.69%	-20.78%	28.48%
Other Income/Expense, Net	$70.00M	$62.00M	$69.00M
YoY Change	12.9%	195.24%	9.52%
Pretax Income	$540.0M	$531.0M	$414.0M
YoY Change	1.69%	137.05%	7.53%
Income Tax	$161.0M	$135.0M	$108.0M
% Of Pretax Income	29.81%	25.42%	26.09%
Net Earnings	$374.0M	$391.0M	$303.0M
YoY Change	-4.35%	155.56%	9.78%
Net Earnings / Revenue	8.47%	9.17%	7.64%
Basic Earnings Per Share	$0.74	$0.77	$0.60
Diluted Earnings Per Share	$0.73	$0.76	$0.59
COMMON SHARES
Basic Shares Outstanding	507.2M shares	504.7M shares	506.0M shares
Diluted Shares Outstanding			511.0M shares

Balance Sheet

Concept	2020 Q4	2019 Q4	2019 Q3
SHORT-TERM ASSETS
Cash & Short-Term Investments	$2.089B	$1.155B	$1.213B
YoY Change	80.87%	8.35%	27.55%
Cash & Equivalents	$2.089B	$1.155B	$1.213B
Short-Term Investments
Other Short-Term Assets	$740.0M	$677.0M	$645.0M
YoY Change	9.31%	22.87%	19.67%
Inventory
Prepaid Expenses
Receivables	$5.326B	$5.236B	$5.198B
Other Receivables	$0.00	$0.00	$0.00
Total Short-Term Assets	$8.155B	$7.068B	$7.056B
YoY Change	15.38%	19.11%	18.27%
LONG-TERM ASSETS
Property, Plant & Equipment	$856.0M	$858.0M	$816.0M
YoY Change	-0.23%	22.4%	15.42%
Goodwill	$15.52B	$14.67B	$14.29B
YoY Change	5.77%	52.84%	51.41%
Intangibles	$2.699B	$2.774B
YoY Change	-2.7%	93.04%
Long-Term Investments	$280.0M	$434.0M	$452.0M
YoY Change	-35.48%	51.22%	52.7%
Other Assets	$1.458B	$1.757B	$1.653B
YoY Change	-17.02%	14.17%	19.7%
Total Long-Term Assets	$24.89B	$24.29B	$24.04B
YoY Change	2.49%	55.26%	58.55%
TOTAL ASSETS
Total Short-Term Assets	$8.155B	$7.068B	$7.056B
Total Long-Term Assets	$24.89B	$24.29B	$24.04B
Total Assets	$33.05B	$31.36B	$31.10B
YoY Change	5.4%	45.32%	47.18%
SHORT-TERM LIABILITIES
YoY Change
Accounts Payable	$3.050B	$2.746B	$2.479B
YoY Change	11.07%	22.92%	8.11%
Accrued Expenses	$2.742B	$2.539B	$2.103B
YoY Change	8.0%	42.8%	49.57%
Deferred Revenue
YoY Change
Short-Term Debt	$517.0M	$1.215B	$625.0M
YoY Change	-57.45%	286.94%	733.33%
Long-Term Debt Due	$517.0M	$1.215B	$514.0M
YoY Change	-57.45%	286.94%	-8.7%
Total Short-Term Liabilities	$6.556B	$6.679B	$6.204B
YoY Change	-1.84%	35.64%	31.25%
LONG-TERM LIABILITIES
Long-Term Debt	$10.80B	$10.74B	$11.43B
YoY Change	0.51%	94.94%	107.35%
Other Long-Term Liabilities	$1.485B	$1.397B	$1.388B
YoY Change	6.3%	2.57%	4.99%
Total Long-Term Liabilities	$12.28B	$12.14B	$12.82B
YoY Change	1.18%	76.63%	869.52%
TOTAL LIABILITIES
Total Short-Term Liabilities	$6.556B	$6.679B	$6.204B
Total Long-Term Liabilities	$12.28B	$12.14B	$12.82B
Total Liabilities	$18.84B	$18.82B	$19.02B
YoY Change	0.11%	59.52%	214.45%
SHAREHOLDERS EQUITY
Retained Earnings	$16.27B	$15.20B	$14.81B
YoY Change	7.06%	5.94%	4.33%
Common Stock	$1.504B	$1.423B	$1.357B
YoY Change	5.69%	3.27%	1.88%
Preferred Stock
YoY Change
Treasury Stock (at cost)	$3.562B	$3.774B	$3.617B
YoY Change	-5.62%	5.8%	0.84%
Treasury Stock Shares	52.91M shares	57.01M shares	55.64M shares
Shareholders Equity	$9.104B	$7.793B	$7.620B
YoY Change
Total Liabilities & Shareholders Equity	$33.05B	$31.36B	$31.10B
YoY Change	5.4%	45.32%	47.18%

Cashflow Statement

Concept	2020 Q4	2019 Q4	2019 Q3
OPERATING ACTIVITIES
Net Income	$374.0M	$391.0M	$303.0M
YoY Change	-4.35%	155.56%	9.78%
Depreciation, Depletion And Amortization	$194.0M	$167.0M	$170.0M
YoY Change	16.17%	35.77%	37.1%
Cash From Operating Activities	$1.383B	$1.070B	$1.050B
YoY Change	29.25%	-3.52%	15.89%
INVESTING ACTIVITIES
Capital Expenditures	-$70.00M	-$137.0M	-$123.0M
YoY Change	-48.91%	48.91%	41.38%
Acquisitions
YoY Change
Other Investing Activities	-$98.00M	-$30.00M	$49.00M
YoY Change	226.67%	-87.76%	-112.69%
Cash From Investing Activities	-$168.0M	-$167.0M	-$74.00M
YoY Change	0.6%	-50.45%	-84.36%
FINANCING ACTIVITIES
Cash Dividend Paid
YoY Change
Common Stock Issuance & Retirement, Net
YoY Change
Debt Paid & Issued, Net
YoY Change
Cash From Financing Activities	-1.717B	-1.031B	-987.0M
YoY Change	66.54%	83.13%	91.65%
NET CHANGE
Cash From Operating Activities	1.383B	1.070B	1.050B
Cash From Investing Activities	-168.0M	-167.0M	-74.00M
Cash From Financing Activities	-1.717B	-1.031B	-987.0M
Net Change In Cash	-502.0M	-128.0M	-11.00M
YoY Change	292.19%	-161.24%	-86.59%
FREE CASH FLOW
Cash From Operating Activities	$1.383B	$1.070B	$1.050B
Capital Expenditures	-$70.00M	-$137.0M	-$123.0M
Free Cash Flow	$1.453B	$1.207B	$1.173B
YoY Change	20.38%	0.5%	18.13%

Facts In Submission

Frame	Concept Type	Concept / XBRL Key	Value	Unit
CY2020	dei	Entity Central Index Key EntityCentralIndexKey	0000062709
CY2020	dei	Document Fiscal Year Focus DocumentFiscalYearFocus	2020
CY2020	dei	Document Fiscal Period Focus DocumentFiscalPeriodFocus	FY
CY2020	dei	Amendment Flag AmendmentFlag	false
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CY2020Q4	us-gaap	Revenue Remaining Performance Obligation Expected Timing Of Satisfaction Period1 RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1	P1Y
CY2020Q4	us-gaap	Revenue Remaining Performance Obligation Expected Timing Of Satisfaction Period1 RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1	P1Y
CY2020Q4	us-gaap	Revenue Remaining Performance Obligation Expected Timing Of Satisfaction Period1 RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1	P1Y
CY2020Q4	us-gaap	Revenue Remaining Performance Obligation Expected Timing Of Satisfaction Period1 RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1
CY2020	dei	Document Type DocumentType	10-K
CY2020	dei	Document Annual Report DocumentAnnualReport	true
CY2020	dei	Entity Tax Identification Number EntityTaxIdentificationNumber	36-2668272
CY2020	dei	Document Period End Date DocumentPeriodEndDate	2020-12-31
CY2020	dei	Current Fiscal Year End Date CurrentFiscalYearEndDate	--12-31
CY2020	dei	Document Transition Report DocumentTransitionReport	false
CY2020	dei	Entity File Number EntityFileNumber	1-5998
CY2020	dei	Entity Registrant Name EntityRegistrantName	Marsh & McLennan Companies, Inc.
CY2020	dei	Entity Incorporation State Country Code EntityIncorporationStateCountryCode	DE
CY2020	dei	Entity Address Address Line1 EntityAddressAddressLine1	1166 Avenue of the Americas
CY2020	dei	Entity Address City Or Town EntityAddressCityOrTown	New York
CY2020	dei	Entity Address State Or Province EntityAddressStateOrProvince	NY
CY2020	dei	Entity Address Postal Zip Code EntityAddressPostalZipCode	10036
CY2020	dei	City Area Code CityAreaCode	212
CY2020	dei	Local Phone Number LocalPhoneNumber	345-5000
CY2020	dei	Security12b Title Security12bTitle	Common Stock, par value $1.00 per share
CY2020	dei	Trading Symbol TradingSymbol	MMC
CY2020	dei	Entity Well Known Seasoned Issuer EntityWellKnownSeasonedIssuer	Yes
CY2020	dei	Entity Voluntary Filers EntityVoluntaryFilers	No
CY2020	dei	Entity Current Reporting Status EntityCurrentReportingStatus	Yes
CY2020	dei	Entity Interactive Data Current EntityInteractiveDataCurrent	Yes
CY2020	dei	Entity Filer Category EntityFilerCategory	Large Accelerated Filer
CY2020	dei	Entity Small Business EntitySmallBusiness	false
CY2020	dei	Entity Emerging Growth Company EntityEmergingGrowthCompany	false
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CY2019Q4	us-gaap	Liabilities Current LiabilitiesCurrent	6679000000	USD
CY2020Q4	mmc	Fiduciary Liabilities Gross Noncurrent FiduciaryLiabilitiesGrossNoncurrent	8585000000	USD
CY2020Q4	mmc	Cashand Investments Heldin Fiduciary Capacity Noncurrent CashandInvestmentsHeldinFiduciaryCapacityNoncurrent	8585000000	USD
CY2019Q4	mmc	Cashand Investments Heldin Fiduciary Capacity Noncurrent CashandInvestmentsHeldinFiduciaryCapacityNoncurrent	7344000000	USD
CY2020Q4	mmc	Fiduciary Liabilities Net Noncurrent FiduciaryLiabilitiesNetNoncurrent	0	USD
CY2019Q4	mmc	Fiduciary Liabilities Net Noncurrent FiduciaryLiabilitiesNetNoncurrent	0	USD
CY2020Q4	us-gaap	Long Term Debt And Capital Lease Obligations LongTermDebtAndCapitalLeaseObligations	10796000000	USD
CY2019Q4	us-gaap	Long Term Debt And Capital Lease Obligations LongTermDebtAndCapitalLeaseObligations	10741000000	USD
CY2020Q4	us-gaap	Pension And Other Postretirement Defined Benefit Plans Liabilities Noncurrent PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent	2662000000	USD
CY2019Q4	us-gaap	Pension And Other Postretirement Defined Benefit Plans Liabilities Noncurrent PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent	2336000000	USD
CY2020Q4	us-gaap	Operating Lease Liability Noncurrent OperatingLeaseLiabilityNoncurrent	1924000000	USD
CY2019Q4	us-gaap	Operating Lease Liability Noncurrent OperatingLeaseLiabilityNoncurrent	1926000000	USD
CY2020Q4	mmc	Liability For Errors And Omissions LiabilityForErrorsAndOmissions	366000000	USD
CY2019Q4	mmc	Liability For Errors And Omissions LiabilityForErrorsAndOmissions	335000000	USD
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CY2019Q4	us-gaap	Other Liabilities Noncurrent OtherLiabilitiesNoncurrent	1397000000	USD
CY2020Q4	us-gaap	Commitments And Contingencies CommitmentsAndContingencies	0	USD
CY2019Q4	us-gaap	Commitments And Contingencies CommitmentsAndContingencies	0	USD
CY2020Q4	us-gaap	Preferred Stock Par Or Stated Value Per Share PreferredStockParOrStatedValuePerShare	1
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CY2020Q4	us-gaap	Preferred Stock Shares Authorized PreferredStockSharesAuthorized	6000000	shares
CY2019Q4	us-gaap	Preferred Stock Shares Authorized PreferredStockSharesAuthorized	6000000	shares
CY2019Q4	us-gaap	Preferred Stock Shares Issued PreferredStockSharesIssued	0	shares
CY2020Q4	us-gaap	Preferred Stock Shares Issued PreferredStockSharesIssued	0	shares
CY2020Q4	us-gaap	Preferred Stock Value PreferredStockValue	0	USD
CY2019Q4	us-gaap	Preferred Stock Value PreferredStockValue	0	USD
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CY2019Q4	us-gaap	Common Stock Par Or Stated Value Per Share CommonStockParOrStatedValuePerShare	1
CY2019Q4	us-gaap	Common Stock Shares Authorized CommonStockSharesAuthorized	1600000000	shares
CY2020Q4	us-gaap	Common Stock Shares Authorized CommonStockSharesAuthorized	1600000000	shares
CY2020Q4	us-gaap	Common Stock Shares Issued CommonStockSharesIssued	560641640	shares
CY2019Q4	us-gaap	Common Stock Shares Issued CommonStockSharesIssued	560641640	shares
CY2020Q4	us-gaap	Common Stock Value CommonStockValue	561000000	USD
CY2019Q4	us-gaap	Common Stock Value CommonStockValue	561000000	USD
CY2020Q4	us-gaap	Additional Paid In Capital Common Stock AdditionalPaidInCapitalCommonStock	943000000	USD
CY2019Q4	us-gaap	Additional Paid In Capital Common Stock AdditionalPaidInCapitalCommonStock	862000000	USD
CY2020Q4	us-gaap	Retained Earnings Accumulated Deficit RetainedEarningsAccumulatedDeficit	16272000000	USD
CY2019Q4	us-gaap	Retained Earnings Accumulated Deficit RetainedEarningsAccumulatedDeficit	15199000000	USD
CY2020Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-5110000000	USD
CY2019Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-5055000000	USD
CY2020Q4	us-gaap	Minority Interest MinorityInterest	156000000	USD
CY2019Q4	us-gaap	Minority Interest MinorityInterest	150000000	USD
CY2020Q4	mmc	Stockholders Equity Subtotal Before Treasury Stock StockholdersEquitySubtotalBeforeTreasuryStock	12822000000	USD
CY2019Q4	mmc	Stockholders Equity Subtotal Before Treasury Stock StockholdersEquitySubtotalBeforeTreasuryStock	11717000000	USD
CY2020Q4	us-gaap	Treasury Stock Shares TreasuryStockShares	52914550	shares
CY2019Q4	us-gaap	Treasury Stock Shares TreasuryStockShares	57013097	shares
CY2020Q4	us-gaap	Treasury Stock Value TreasuryStockValue	3562000000	USD
CY2019Q4	us-gaap	Treasury Stock Value TreasuryStockValue	3774000000	USD
CY2020Q4	us-gaap	Stockholders Equity Including Portion Attributable To Noncontrolling Interest StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	9260000000	USD
CY2019Q4	us-gaap	Stockholders Equity Including Portion Attributable To Noncontrolling Interest StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	7943000000	USD
CY2020Q4	us-gaap	Liabilities And Stockholders Equity LiabilitiesAndStockholdersEquity	33049000000	USD
CY2019Q4	us-gaap	Liabilities And Stockholders Equity LiabilitiesAndStockholdersEquity	31357000000	USD
CY2020	us-gaap	Profit Loss ProfitLoss	2046000000	USD
CY2019	us-gaap	Profit Loss ProfitLoss	1773000000	USD
CY2018	us-gaap	Profit Loss ProfitLoss	1670000000	USD
CY2020	us-gaap	Depreciation Depreciation	390000000	USD
CY2019	us-gaap	Depreciation Depreciation	333000000	USD
CY2018	us-gaap	Depreciation Depreciation	311000000	USD
CY2020	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	351000000	USD
CY2019	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	314000000	USD
CY2018	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	183000000	USD
CY2020	mmc	Leases Right Of Use Asset Amortization LeasesRightOfUseAssetAmortization	355000000	USD
CY2019	mmc	Leases Right Of Use Asset Amortization LeasesRightOfUseAssetAmortization	315000000	USD
CY2018	mmc	Leases Right Of Use Asset Amortization LeasesRightOfUseAssetAmortization	0	USD
CY2020	us-gaap	Business Combination Contingent Consideration Arrangements Change In Amount Of Contingent Consideration Liability1 BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1	-22000000	USD
CY2019	us-gaap	Business Combination Contingent Consideration Arrangements Change In Amount Of Contingent Consideration Liability1 BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1	27000000	USD
CY2018	us-gaap	Business Combination Contingent Consideration Arrangements Change In Amount Of Contingent Consideration Liability1 BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1	-4000000	USD
CY2020	us-gaap	Deconsolidation Gain Or Loss Amount DeconsolidationGainOrLossAmount	0	USD
CY2019	us-gaap	Deconsolidation Gain Or Loss Amount DeconsolidationGainOrLossAmount	0	USD
CY2018	us-gaap	Deconsolidation Gain Or Loss Amount DeconsolidationGainOrLossAmount	-11000000	USD
CY2020	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	0	USD
CY2019	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	-32000000	USD
CY2018	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	0	USD
CY2020	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	40000000	USD
CY2019	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	84000000	USD
CY2018	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	-39000000	USD
CY2020	us-gaap	Gain Loss On Investments GainLossOnInvestments	-22000000	USD
CY2019	us-gaap	Gain Loss On Investments GainLossOnInvestments	22000000	USD
CY2018	us-gaap	Gain Loss On Investments GainLossOnInvestments	-12000000	USD
CY2020	us-gaap	Gain Loss On Sale Of Other Assets GainLossOnSaleOfOtherAssets	-24000000	USD
CY2019	us-gaap	Gain Loss On Sale Of Other Assets GainLossOnSaleOfOtherAssets	-56000000	USD
CY2018	us-gaap	Gain Loss On Sale Of Other Assets GainLossOnSaleOfOtherAssets	48000000	USD
CY2020	us-gaap	Share Based Compensation ShareBasedCompensation	290000000	USD
CY2019	us-gaap	Share Based Compensation ShareBasedCompensation	252000000	USD
CY2018	us-gaap	Share Based Compensation ShareBasedCompensation	193000000	USD
CY2020	mmc	Acquisition Related Hedging Expense AcquisitionRelatedHedgingExpense	0	USD
CY2019	mmc	Acquisition Related Hedging Expense AcquisitionRelatedHedgingExpense	8000000	USD
CY2018	mmc	Acquisition Related Hedging Expense AcquisitionRelatedHedgingExpense	441000000	USD
CY2020	us-gaap	Increase Decrease In Receivables IncreaseDecreaseInReceivables	75000000	USD
CY2019	us-gaap	Increase Decrease In Receivables IncreaseDecreaseInReceivables	130000000	USD
CY2018	us-gaap	Increase Decrease In Receivables IncreaseDecreaseInReceivables	78000000	USD
CY2020	us-gaap	Increase Decrease In Other Current Assets IncreaseDecreaseInOtherCurrentAssets	66000000	USD
CY2019	us-gaap	Increase Decrease In Other Current Assets IncreaseDecreaseInOtherCurrentAssets	13000000	USD
CY2018	us-gaap	Increase Decrease In Other Current Assets IncreaseDecreaseInOtherCurrentAssets	-26000000	USD
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CY2019	us-gaap	Increase Decrease In Other Noncurrent Assets IncreaseDecreaseInOtherNoncurrentAssets	1000000	USD
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CY2020	us-gaap	Increase Decrease In Accounts Payable And Accrued Liabilities IncreaseDecreaseInAccountsPayableAndAccruedLiabilities	241000000	USD
CY2019	us-gaap	Increase Decrease In Accounts Payable And Accrued Liabilities IncreaseDecreaseInAccountsPayableAndAccruedLiabilities	120000000	USD
CY2018	us-gaap	Increase Decrease In Accounts Payable And Accrued Liabilities IncreaseDecreaseInAccountsPayableAndAccruedLiabilities	23000000	USD
CY2020	us-gaap	Increase Decrease In Employee Related Liabilities IncreaseDecreaseInEmployeeRelatedLiabilities	207000000	USD
CY2019	us-gaap	Increase Decrease In Employee Related Liabilities IncreaseDecreaseInEmployeeRelatedLiabilities	154000000	USD
CY2018	us-gaap	Increase Decrease In Employee Related Liabilities IncreaseDecreaseInEmployeeRelatedLiabilities	68000000	USD
CY2020	us-gaap	Increase Decrease In Accrued Income Taxes Payable IncreaseDecreaseInAccruedIncomeTaxesPayable	60000000	USD
CY2019	us-gaap	Increase Decrease In Accrued Income Taxes Payable IncreaseDecreaseInAccruedIncomeTaxesPayable	42000000	USD
CY2018	us-gaap	Increase Decrease In Accrued Income Taxes Payable IncreaseDecreaseInAccruedIncomeTaxesPayable	-40000000	USD
CY2020	mmc	Pensionand Other Postretirement Benefit Contributions In Excessof Current Year Expense PensionandOtherPostretirementBenefitContributionsInExcessofCurrentYearExpense	356000000	USD
CY2019	mmc	Pensionand Other Postretirement Benefit Contributions In Excessof Current Year Expense PensionandOtherPostretirementBenefitContributionsInExcessofCurrentYearExpense	369000000	USD
CY2018	mmc	Pensionand Other Postretirement Benefit Contributions In Excessof Current Year Expense PensionandOtherPostretirementBenefitContributionsInExcessofCurrentYearExpense	291000000	USD
CY2020	us-gaap	Increase Decrease In Other Operating Liabilities IncreaseDecreaseInOtherOperatingLiabilities	108000000	USD
CY2019	us-gaap	Increase Decrease In Other Operating Liabilities IncreaseDecreaseInOtherOperatingLiabilities	-172000000	USD
CY2018	us-gaap	Increase Decrease In Other Operating Liabilities IncreaseDecreaseInOtherOperatingLiabilities	9000000	USD
CY2020	mmc	Increase Decreasein Operating Lease Liabilities IncreaseDecreaseinOperatingLeaseLiabilities	-351000000	USD
CY2019	mmc	Increase Decreasein Operating Lease Liabilities IncreaseDecreaseinOperatingLeaseLiabilities	-327000000	USD
CY2018	mmc	Increase Decreasein Operating Lease Liabilities IncreaseDecreaseinOperatingLeaseLiabilities	0	USD
CY2020	mmc	Effectof Exchange Rateon Cashand Cash Equivalentsfrom Operating Activities EffectofExchangeRateonCashandCashEquivalentsfromOperatingActivities	32000000	USD
CY2019	mmc	Effectof Exchange Rateon Cashand Cash Equivalentsfrom Operating Activities EffectofExchangeRateonCashandCashEquivalentsfromOperatingActivities	-115000000	USD
CY2018	mmc	Effectof Exchange Rateon Cashand Cash Equivalentsfrom Operating Activities EffectofExchangeRateonCashandCashEquivalentsfromOperatingActivities	18000000	USD
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CY2019	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	2361000000	USD
CY2018	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	2428000000	USD
CY2020	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	0	USD
CY2019	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	485000000	USD
CY2018	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	675000000	USD
CY2020	us-gaap	Proceeds From Repayments Of Short Term Debt ProceedsFromRepaymentsOfShortTermDebt	1000000000	USD
CY2019	us-gaap	Proceeds From Repayments Of Short Term Debt ProceedsFromRepaymentsOfShortTermDebt	300000000	USD
CY2018	us-gaap	Proceeds From Repayments Of Short Term Debt ProceedsFromRepaymentsOfShortTermDebt	0	USD
CY2020	us-gaap	Proceeds From Issuance Of Debt ProceedsFromIssuanceOfDebt	737000000	USD
CY2019	us-gaap	Proceeds From Issuance Of Debt ProceedsFromIssuanceOfDebt	6459000000	USD
CY2018	us-gaap	Proceeds From Issuance Of Debt ProceedsFromIssuanceOfDebt	591000000	USD
CY2020	us-gaap	Repayments Of Long Term Debt RepaymentsOfLongTermDebt	2515000000	USD
CY2019	us-gaap	Repayments Of Long Term Debt RepaymentsOfLongTermDebt	1064000000	USD
CY2018	us-gaap	Repayments Of Long Term Debt RepaymentsOfLongTermDebt	263000000	USD
CY2020	us-gaap	Payments Of Financing Costs PaymentsOfFinancingCosts	0	USD
CY2019	us-gaap	Payments Of Financing Costs PaymentsOfFinancingCosts	0	USD
CY2018	us-gaap	Payments Of Financing Costs PaymentsOfFinancingCosts	35000000	USD
CY2020	us-gaap	Payments Of Debt Extinguishment Costs PaymentsOfDebtExtinguishmentCosts	0	USD
CY2019	us-gaap	Payments Of Debt Extinguishment Costs PaymentsOfDebtExtinguishmentCosts	585000000	USD
CY2018	us-gaap	Payments Of Debt Extinguishment Costs PaymentsOfDebtExtinguishmentCosts	0	USD
CY2020	us-gaap	Payments To Acquire Additional Interest In Subsidiaries PaymentsToAcquireAdditionalInterestInSubsidiaries	3000000	USD
CY2019	us-gaap	Payments To Acquire Additional Interest In Subsidiaries PaymentsToAcquireAdditionalInterestInSubsidiaries	80000000	USD
CY2018	us-gaap	Payments To Acquire Additional Interest In Subsidiaries PaymentsToAcquireAdditionalInterestInSubsidiaries	0	USD
CY2020	us-gaap	Payments For Derivative Instrument Financing Activities PaymentsForDerivativeInstrumentFinancingActivities	0	USD
CY2019	us-gaap	Payments For Derivative Instrument Financing Activities PaymentsForDerivativeInstrumentFinancingActivities	337000000	USD
CY2018	us-gaap	Payments For Derivative Instrument Financing Activities PaymentsForDerivativeInstrumentFinancingActivities	0	USD
CY2020	us-gaap	Payments Related To Tax Withholding For Share Based Compensation PaymentsRelatedToTaxWithholdingForShareBasedCompensation	132000000	USD
CY2019	us-gaap	Payments Related To Tax Withholding For Share Based Compensation PaymentsRelatedToTaxWithholdingForShareBasedCompensation	89000000	USD
CY2018	us-gaap	Payments Related To Tax Withholding For Share Based Compensation PaymentsRelatedToTaxWithholdingForShareBasedCompensation	67000000	USD
CY2020	us-gaap	Proceeds From Issuance Or Sale Of Equity ProceedsFromIssuanceOrSaleOfEquity	132000000	USD
CY2019	us-gaap	Proceeds From Issuance Or Sale Of Equity ProceedsFromIssuanceOrSaleOfEquity	158000000	USD
CY2018	us-gaap	Proceeds From Issuance Or Sale Of Equity ProceedsFromIssuanceOrSaleOfEquity	93000000	USD
CY2020	mmc	Paymentsfor Acquisitions Deferredand Contingent Consideration PaymentsforAcquisitionsDeferredandContingentConsideration	122000000	USD
CY2019	mmc	Paymentsfor Acquisitions Deferredand Contingent Consideration PaymentsforAcquisitionsDeferredandContingentConsideration	65000000	USD
CY2018	mmc	Paymentsfor Acquisitions Deferredand Contingent Consideration PaymentsforAcquisitionsDeferredandContingentConsideration	117000000	USD
CY2020	us-gaap	Payments To Minority Shareholders PaymentsToMinorityShareholders	34000000	USD
CY2019	us-gaap	Payments To Minority Shareholders PaymentsToMinorityShareholders	16000000	USD
CY2018	us-gaap	Payments To Minority Shareholders PaymentsToMinorityShareholders	30000000	USD
CY2020	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	943000000	USD
CY2019	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	890000000	USD
CY2018	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	807000000	USD
CY2020	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	-1880000000	USD
CY2019	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	3306000000	USD
CY2018	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	-1310000000	USD
CY2020	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	348000000	USD
CY2019	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	421000000	USD
CY2018	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	314000000	USD
CY2020	us-gaap	Payments For Proceeds From Investments PaymentsForProceedsFromInvestments	-107000000	USD
CY2019	us-gaap	Payments For Proceeds From Investments PaymentsForProceedsFromInvestments	-183000000	USD
CY2018	us-gaap	Payments For Proceeds From Investments PaymentsForProceedsFromInvestments	-4000000	USD
CY2020	us-gaap	Payments To Acquire Equity Method Investments PaymentsToAcquireEquityMethodInvestments	0	USD
CY2019	us-gaap	Payments To Acquire Equity Method Investments PaymentsToAcquireEquityMethodInvestments	91000000	USD
CY2018	us-gaap	Payments To Acquire Equity Method Investments PaymentsToAcquireEquityMethodInvestments	0	USD
CY2020	us-gaap	Proceeds From Sale Of Property Plant And Equipment ProceedsFromSaleOfPropertyPlantAndEquipment	6000000	USD
CY2019	us-gaap	Proceeds From Sale Of Property Plant And Equipment ProceedsFromSaleOfPropertyPlantAndEquipment	10000000	USD
CY2018	us-gaap	Proceeds From Sale Of Property Plant And Equipment ProceedsFromSaleOfPropertyPlantAndEquipment	3000000	USD
CY2020	us-gaap	Proceeds From Divestiture Of Businesses And Interests In Affiliates ProceedsFromDivestitureOfBusinessesAndInterestsInAffiliates	98000000	USD
CY2019	us-gaap	Proceeds From Divestiture Of Businesses And Interests In Affiliates ProceedsFromDivestitureOfBusinessesAndInterestsInAffiliates	229000000	USD
CY2018	us-gaap	Proceeds From Divestiture Of Businesses And Interests In Affiliates ProceedsFromDivestitureOfBusinessesAndInterestsInAffiliates	110000000	USD
CY2020	us-gaap	Payments To Acquire Businesses Net Of Cash Acquired PaymentsToAcquireBusinessesNetOfCashAcquired	668000000	USD
CY2019	us-gaap	Payments To Acquire Businesses Net Of Cash Acquired PaymentsToAcquireBusinessesNetOfCashAcquired	5505000000	USD
CY2018	us-gaap	Payments To Acquire Businesses Net Of Cash Acquired PaymentsToAcquireBusinessesNetOfCashAcquired	884000000	USD
CY2020	us-gaap	Payments For Proceeds From Other Investing Activities PaymentsForProceedsFromOtherInvestingActivities	9000000	USD
CY2019	us-gaap	Payments For Proceeds From Other Investing Activities PaymentsForProceedsFromOtherInvestingActivities	76000000	USD
CY2018	us-gaap	Payments For Proceeds From Other Investing Activities PaymentsForProceedsFromOtherInvestingActivities	8000000	USD
CY2020	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-814000000	USD
CY2019	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-5671000000	USD
CY2018	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-1089000000	USD
CY2020	us-gaap	Effect Of Exchange Rate On Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	246000000	USD
CY2019	us-gaap	Effect Of Exchange Rate On Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	93000000	USD
CY2018	us-gaap	Effect Of Exchange Rate On Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	-168000000	USD
CY2020	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	934000000	USD
CY2019	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	89000000	USD
CY2018	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	-139000000	USD
CY2019Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	1155000000	USD
CY2018Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	1066000000	USD
CY2017Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	1205000000	USD
CY2020Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	2089000000	USD
CY2019Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	1155000000	USD
CY2018Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	1066000000	USD
CY2020	mmc	Dividend Equivalents Per Share Cash Declared DividendEquivalentsPerShareCashDeclared	1.84
CY2019	mmc	Dividend Equivalents Per Share Cash Declared DividendEquivalentsPerShareCashDeclared	1.74
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CY2020	mmc	Common Stock Dividends Per Share Cash Declared CommonStockDividendsPerShareCashDeclared	1.84
CY2019	mmc	Common Stock Dividends Per Share Cash Declared CommonStockDividendsPerShareCashDeclared	1.74
CY2018	mmc	Common Stock Dividends Per Share Cash Declared CommonStockDividendsPerShareCashDeclared	1.58
CY2020Q4	us-gaap	Stockholders Equity Including Portion Attributable To Noncontrolling Interest StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	9260000000	USD
CY2019Q4	us-gaap	Stockholders Equity Including Portion Attributable To Noncontrolling Interest StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	7943000000	USD
CY2018Q4	us-gaap	Stockholders Equity Including Portion Attributable To Noncontrolling Interest StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	7584000000	USD
CY2019	us-gaap	Income Loss From Equity Method Investments IncomeLossFromEquityMethodInvestments	12000000	USD
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CY2020Q4	us-gaap	Restricted Cash And Cash Equivalents At Carrying Value RestrictedCashAndCashEquivalentsAtCarryingValue	270000000	USD
CY2020Q4	us-gaap	Property Plant And Equipment Gross PropertyPlantAndEquipmentGross	3015000000	USD
CY2019Q4	us-gaap	Property Plant And Equipment Gross PropertyPlantAndEquipmentGross	2859000000	USD
CY2020Q4	us-gaap	Accumulated Depreciation Depletion And Amortization Property Plant And Equipment AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	2159000000	USD
CY2019Q4	us-gaap	Accumulated Depreciation Depletion And Amortization Property Plant And Equipment AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	2001000000	USD
CY2020Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	856000000	USD
CY2019Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	858000000	USD
CY2020	us-gaap	Gain Loss On Investments GainLossOnInvestments	-22000000	USD
CY2019	us-gaap	Gain Loss On Investments GainLossOnInvestments	22000000	USD
CY2018	us-gaap	Gain Loss On Investments GainLossOnInvestments	-12000000	USD
CY2019	us-gaap	Equity Securities Fv Ni Realized Gain Loss EquitySecuritiesFvNiRealizedGainLoss	10000000	USD
CY2018	us-gaap	Equity Securities Fv Ni Realized Gain Loss EquitySecuritiesFvNiRealizedGainLoss	54000000	USD
CY2018	us-gaap	Income Loss From Equity Method Investments IncomeLossFromEquityMethodInvestments	17000000	USD
CY2019Q4	us-gaap	Indefinite Lived Intangible Assets Excluding Goodwill IndefiniteLivedIntangibleAssetsExcludingGoodwill	0	USD
CY2020Q4	us-gaap	Indefinite Lived Intangible Assets Excluding Goodwill IndefiniteLivedIntangibleAssetsExcludingGoodwill	0	USD
CY2020Q4	us-gaap	Capitalized Computer Software Net CapitalizedComputerSoftwareNet	481000000	USD
CY2019Q4	us-gaap	Capitalized Computer Software Net CapitalizedComputerSoftwareNet	496000000	USD
CY2020Q4	us-gaap	Capitalized Computer Software Accumulated Amortization CapitalizedComputerSoftwareAccumulatedAmortization	1600000000	USD
CY2019Q4	us-gaap	Capitalized Computer Software Accumulated Amortization CapitalizedComputerSoftwareAccumulatedAmortization	1400000000	USD
CY2020Q4	mmc	Liability For Errors And Omissions Current And Noncurrent LiabilityForErrorsAndOmissionsCurrentAndNoncurrent	639000000	USD
CY2019Q4	mmc	Liability For Errors And Omissions Current And Noncurrent LiabilityForErrorsAndOmissionsCurrentAndNoncurrent	484000000	USD
CY2020	us-gaap	Concentration Risk Credit Risk ConcentrationRiskCreditRisk	<span style="color:#000000;font-family:'Arial',sans-serif;font-size:10pt;font-weight:700;line-height:120%">Concentrations of Credit Risk: </span><span style="color:#000000;font-family:'Arial',sans-serif;font-size:10pt;font-weight:400;line-height:120%">Financial instruments which potentially subject the Company to concentrations of credit risk consist primarily of cash and cash equivalents, commissions and fees receivable and insurance recoverables. The Company maintains a policy providing for the diversification of cash and cash equivalent investments and places its investments in a large number of high quality financial institutions to limit the amount of credit risk exposure. Concentrations of credit risk with respect to receivables are generally limited due to the large number of clients and markets in which the Company does business, as well as the dispersion across many geographic areas.</span>
CY2020	us-gaap	Profit Loss ProfitLoss	2046000000	USD
CY2019	us-gaap	Profit Loss ProfitLoss	1773000000	USD
CY2018	us-gaap	Profit Loss ProfitLoss	1670000000	USD
CY2020	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	30000000	USD
CY2019	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	31000000	USD
CY2018	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	20000000	USD
CY2020	us-gaap	Net Income Loss NetIncomeLoss	2016000000	USD
CY2019	us-gaap	Net Income Loss NetIncomeLoss	1742000000	USD
CY2018	us-gaap	Net Income Loss NetIncomeLoss	1650000000	USD
CY2020	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	506000000	shares
CY2019	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	506000000	shares
CY2018	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	506000000	shares
CY2020	us-gaap	Weighted Average Number Diluted Shares Outstanding Adjustment WeightedAverageNumberDilutedSharesOutstandingAdjustment	6000000	shares
CY2019	us-gaap	Weighted Average Number Diluted Shares Outstanding Adjustment WeightedAverageNumberDilutedSharesOutstandingAdjustment	5000000	shares
CY2018	us-gaap	Weighted Average Number Diluted Shares Outstanding Adjustment WeightedAverageNumberDilutedSharesOutstandingAdjustment	5000000	shares
CY2020	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	512000000	shares
CY2019	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	511000000	shares
CY2018	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	511000000	shares
CY2020	mmc	Average Share Price Common Stock AverageSharePriceCommonStock	109.12
CY2019	mmc	Average Share Price Common Stock AverageSharePriceCommonStock	97.23
CY2018	mmc	Average Share Price Common Stock AverageSharePriceCommonStock	83.13
CY2020Q4	mmc	Uncollected Premiumsand Claims Netof Related Payables UncollectedPremiumsandClaimsNetofRelatedPayables	11200000000	USD
CY2019Q4	mmc	Uncollected Premiumsand Claims Netof Related Payables UncollectedPremiumsandClaimsNetofRelatedPayables	8900000000	USD
CY2020	us-gaap	Use Of Estimates UseOfEstimates	<span style="background-color:#ffffff;color:#000000;font-family:'Arial',sans-serif;font-size:10pt;font-weight:700;line-height:120%">Estimates:</span><span style="background-color:#ffffff;color:#000000;font-family:'Arial',sans-serif;font-size:10pt;font-weight:400;line-height:120%"> The preparation of the consolidated financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expense during the reporting period. On an ongoing basis, the Company evaluates its estimates, judgments and methodologies. The estimates are based on historical experience and on various other assumptions that the Company believes are reasonable. Such matters include:</span><div style="margin-top:5pt;padding-left:60.75pt;text-indent:-18pt"><span style="background-color:#ffffff;color:#000000;font-family:'Arial',sans-serif;font-size:10pt;font-weight:400;line-height:120%">•</span><span style="background-color:#ffffff;color:#000000;font-family:'Arial',sans-serif;font-size:10pt;font-weight:400;line-height:120%;padding-left:14.5pt">the allowance for current expected credit losses on receivables, </span></div><div style="margin-top:5pt;padding-left:60.75pt;text-indent:-18pt"><span style="background-color:#ffffff;color:#000000;font-family:'Arial',sans-serif;font-size:10pt;font-weight:400;line-height:120%">•</span><span style="background-color:#ffffff;color:#000000;font-family:'Arial',sans-serif;font-size:10pt;font-weight:400;line-height:120%;padding-left:14.5pt">estimates of revenue, </span></div><div style="margin-top:5pt;padding-left:60.75pt;text-indent:-18pt"><span style="background-color:#ffffff;color:#000000;font-family:'Arial',sans-serif;font-size:10pt;font-weight:400;line-height:120%">•</span><span style="background-color:#ffffff;color:#000000;font-family:'Arial',sans-serif;font-size:10pt;font-weight:400;line-height:120%;padding-left:14.5pt">impairment assessments and charges, </span></div><div style="margin-top:5pt;padding-left:60.75pt;text-indent:-18pt"><span style="background-color:#ffffff;color:#000000;font-family:'Arial',sans-serif;font-size:10pt;font-weight:400;line-height:120%">•</span><span style="background-color:#ffffff;color:#000000;font-family:'Arial',sans-serif;font-size:10pt;font-weight:400;line-height:120%;padding-left:14.5pt">recoverability of long-lived assets,</span></div><div style="margin-top:5pt;padding-left:60.75pt;text-indent:-18pt"><span style="background-color:#ffffff;color:#000000;font-family:'Arial',sans-serif;font-size:10pt;font-weight:400;line-height:120%">•</span><span style="background-color:#ffffff;color:#000000;font-family:'Arial',sans-serif;font-size:10pt;font-weight:400;line-height:120%;padding-left:14.5pt">liabilities for errors and omissions,</span></div><div style="margin-top:5pt;padding-left:60.75pt;text-indent:-18pt"><span style="background-color:#ffffff;color:#000000;font-family:'Arial',sans-serif;font-size:10pt;font-weight:400;line-height:120%">•</span><span style="background-color:#ffffff;color:#000000;font-family:'Arial',sans-serif;font-size:10pt;font-weight:400;line-height:120%;padding-left:14.5pt">deferred tax assets, uncertain tax positions and income tax expense, </span></div><div style="margin-top:5pt;padding-left:60.75pt;text-indent:-18pt"><span style="background-color:#ffffff;color:#000000;font-family:'Arial',sans-serif;font-size:10pt;font-weight:400;line-height:120%">•</span><span style="background-color:#ffffff;color:#000000;font-family:'Arial',sans-serif;font-size:10pt;font-weight:400;line-height:120%;padding-left:14.5pt">share-based and incentive compensation expense, </span></div><div style="margin-top:5pt;padding-left:60.75pt;text-indent:-18pt"><span style="background-color:#ffffff;color:#000000;font-family:'Arial',sans-serif;font-size:10pt;font-weight:400;line-height:120%">•</span><span style="background-color:#ffffff;color:#000000;font-family:'Arial',sans-serif;font-size:10pt;font-weight:400;line-height:120%;padding-left:14.5pt">useful lives assigned to long-lived assets, and depreciation and amortization,</span></div><div style="margin-top:5pt;padding-left:60.75pt;text-indent:-18pt"><span style="background-color:#ffffff;color:#000000;font-family:'Arial',sans-serif;font-size:10pt;font-weight:400;line-height:120%">•</span><span style="background-color:#ffffff;color:#000000;font-family:'Arial',sans-serif;font-size:10pt;font-weight:400;line-height:120%;padding-left:14.5pt">fair value estimates of contingent consideration receivable or payable related to acquisitions or dispositions </span></div><div style="margin-top:5pt"><span style="background-color:#ffffff;color:#000000;font-family:'Arial',sans-serif;font-size:10pt;font-weight:400;line-height:120%">The Company believes these estimates are reasonable based on information currently available at the time they are made. In most situations where estimates, fair values or recoverability of assets is dependent upon short or long term projections of cash flows, revenues or earnings before interest, taxes, depreciation and amortization ("EBITDA"), the Company has based its projections assuming the gradual lifting of global lockdowns during 2021. The Company has also considered potential impacts to its customer base in various industries and geographies. The ultimate extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s businesses, results of operations and financial condition will depend on future developments that are highly uncertain, including new information that may emerge concerning COVID-19 and the actions taken to contain it or treat it, and the economic impact on local, regional, national and international customers and markets. Actual results may differ from these estimates.</span></div>
CY2020	mmc	Revenue Percent RevenuePercent	0.01
CY2020	mmc	Brokerage Revenue Number Of Annual Installments BrokerageRevenueNumberOfAnnualInstallments	4	installment
CY2020Q4	us-gaap	Contract With Customer Asset Net ContractWithCustomerAssetNet	236000000	USD
CY2019Q4	us-gaap	Contract With Customer Asset Net ContractWithCustomerAssetNet	207000000	USD
CY2018Q4	us-gaap	Contract With Customer Asset Net ContractWithCustomerAssetNet	112000000	USD
CY2020Q4	us-gaap	Contract With Customer Liability ContractWithCustomerLiability	676000000	USD
CY2019Q4	us-gaap	Contract With Customer Liability ContractWithCustomerLiability	593000000	USD
CY2018Q4	us-gaap	Contract With Customer Liability ContractWithCustomerLiability	545000000	USD
CY2020	us-gaap	Contract With Customer Asset Cumulative Catch Up Adjustment To Revenue Change In Measure Of Progress ContractWithCustomerAssetCumulativeCatchUpAdjustmentToRevenueChangeInMeasureOfProgress	311000000	USD
CY2020	us-gaap	Contract With Customer Asset Reclassified To Receivable ContractWithCustomerAssetReclassifiedToReceivable	284000000	USD
CY2019	us-gaap	Contract With Customer Asset Cumulative Catch Up Adjustment To Revenue Change In Measure Of Progress ContractWithCustomerAssetCumulativeCatchUpAdjustmentToRevenueChangeInMeasureOfProgress	437000000	USD
CY2019	us-gaap	Contract With Customer Asset Reclassified To Receivable ContractWithCustomerAssetReclassifiedToReceivable	342000000	USD
CY2020	mmc	Contractwith Customer Liability Increase Decreasefor Cash Receivedfor Performance Obligations Not Yet Fulfilled ContractwithCustomerLiabilityIncreaseDecreaseforCashReceivedforPerformanceObligationsNotYetFulfilled	615000000	USD
CY2020	us-gaap	Contract With Customer Liability Revenue Recognized ContractWithCustomerLiabilityRevenueRecognized	527000000	USD
CY2019	us-gaap	Contract With Customer Liability Revenue Recognized ContractWithCustomerLiabilityRevenueRecognized	531000000	USD
CY2020	us-gaap	Contract With Customer Liability Cumulative Catch Up Adjustment To Revenue Change In Estimate Of Transaction Price ContractWithCustomerLiabilityCumulativeCatchUpAdjustmentToRevenueChangeInEstimateOfTransactionPrice	-42000000	USD
CY2020	us-gaap	Contract With Customer Performance Obligation Satisfied In Previous Period ContractWithCustomerPerformanceObligationSatisfiedInPreviousPeriod	97000000	USD
CY2019	us-gaap	Contract With Customer Performance Obligation Satisfied In Previous Period ContractWithCustomerPerformanceObligationSatisfiedInPreviousPeriod	79000000	USD
CY2020Q4	us-gaap	Revenue Remaining Performance Obligation RevenueRemainingPerformanceObligation	135000000	USD
CY2020Q4	us-gaap	Revenue Remaining Performance Obligation RevenueRemainingPerformanceObligation	64000000	USD
CY2020Q4	us-gaap	Revenue Remaining Performance Obligation RevenueRemainingPerformanceObligation	22000000	USD
CY2020Q4	us-gaap	Revenue Remaining Performance Obligation RevenueRemainingPerformanceObligation	6000000	USD
CY2020Q4	us-gaap	Revenue Remaining Performance Obligation RevenueRemainingPerformanceObligation	1000000	USD
CY2020	us-gaap	Capitalized Contract Cost Amortization CapitalizedContractCostAmortization	1300000000	USD
CY2019	us-gaap	Capitalized Contract Cost Amortization CapitalizedContractCostAmortization	1200000000	USD
CY2020	mmc	Business Combination Consideration Transferred Assets Acquired BusinessCombinationConsiderationTransferredAssetsAcquired	929000000	USD
CY2019	mmc	Business Combination Consideration Transferred Assets Acquired BusinessCombinationConsiderationTransferredAssetsAcquired	8655000000	USD
CY2018	mmc	Business Combination Consideration Transferred Assets Acquired BusinessCombinationConsiderationTransferredAssetsAcquired	1100000000	USD
CY2020	us-gaap	Business Combination Consideration Transferred Liabilities Incurred BusinessCombinationConsiderationTransferredLiabilitiesIncurred	78000000	USD
CY2019	us-gaap	Business Combination Consideration Transferred Liabilities Incurred BusinessCombinationConsiderationTransferredLiabilitiesIncurred	2804000000	USD
CY2018	us-gaap	Business Combination Consideration Transferred Liabilities Incurred BusinessCombinationConsiderationTransferredLiabilitiesIncurred	83000000	USD
CY2020	mmc	Business Combination Consideration Transferred Noncontrolling Interests Assumed BusinessCombinationConsiderationTransferredNoncontrollingInterestsAssumed	0	USD
CY2019	mmc	Business Combination Consideration Transferred Noncontrolling Interests Assumed BusinessCombinationConsiderationTransferredNoncontrollingInterestsAssumed	280000000	USD
CY2018	mmc	Business Combination Consideration Transferred Noncontrolling Interests Assumed BusinessCombinationConsiderationTransferredNoncontrollingInterestsAssumed	0	USD
CY2020	mmc	Business Combination Contingentand Deferred Consideration BusinessCombinationContingentandDeferredConsideration	183000000	USD
CY2019	mmc	Business Combination Contingentand Deferred Consideration BusinessCombinationContingentandDeferredConsideration	66000000	USD
CY2018	mmc	Business Combination Contingentand Deferred Consideration BusinessCombinationContingentandDeferredConsideration	133000000	USD
CY2020	us-gaap	Payments To Acquire Businesses Net Of Cash Acquired PaymentsToAcquireBusinessesNetOfCashAcquired	668000000	USD
CY2019	us-gaap	Payments To Acquire Businesses Net Of Cash Acquired PaymentsToAcquireBusinessesNetOfCashAcquired	5505000000	USD
CY2018	us-gaap	Payments To Acquire Businesses Net Of Cash Acquired PaymentsToAcquireBusinessesNetOfCashAcquired	884000000	USD
CY2020	us-gaap	Interest Paid Net InterestPaidNet	481000000	USD
CY2019	us-gaap	Interest Paid Net InterestPaidNet	427000000	USD
CY2018	us-gaap	Interest Paid Net InterestPaidNet	264000000	USD
CY2020	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	673000000	USD
CY2019	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	661000000	USD
CY2018	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	632000000	USD
CY2020	mmc	Payments For Previous Acquisition Deferredand Contingent Consideration PaymentsForPreviousAcquisitionDeferredandContingentConsideration	122000000	USD
CY2020	mmc	Payments For Previous Acquisition Deferred Consideration PaymentsForPreviousAcquisitionDeferredConsideration	68000000	USD
CY2020	mmc	Payments For Previous Acquisition Contingent Consideration PaymentsForPreviousAcquisitionContingentConsideration	54000000	USD
CY2019	mmc	Payments For Previous Acquisition Deferredand Contingent Consideration PaymentsForPreviousAcquisitionDeferredandContingentConsideration	65000000	USD
CY2019	mmc	Payments For Previous Acquisition Deferred Consideration PaymentsForPreviousAcquisitionDeferredConsideration	43000000	USD
CY2019	mmc	Payments For Previous Acquisition Contingent Consideration PaymentsForPreviousAcquisitionContingentConsideration	22000000	USD
CY2018	mmc	Payments For Previous Acquisition Deferredand Contingent Consideration PaymentsForPreviousAcquisitionDeferredandContingentConsideration	117000000	USD
CY2018	mmc	Payments For Previous Acquisition Deferred Consideration PaymentsForPreviousAcquisitionDeferredConsideration	62000000	USD
CY2018	mmc	Payments For Previous Acquisition Contingent Consideration PaymentsForPreviousAcquisitionContingentConsideration	55000000	USD
CY2020	mmc	Fair Value Measurementwith Unobservable Inputs Reconciliation Recurring Basis Liability Gain Loss Includedin Earnings Net FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedinEarningsNet	26000000	USD
CY2020	mmc	Paymentof Contingent Consideration PaymentofContingentConsideration	48000000	USD
CY2019	mmc	Fair Value Measurementwith Unobservable Inputs Reconciliation Recurring Basis Liability Gain Loss Includedin Earnings Net FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedinEarningsNet	68000000	USD
CY2019	mmc	Paymentof Contingent Consideration PaymentofContingentConsideration	41000000	USD
CY2018	mmc	Fair Value Measurementwith Unobservable Inputs Reconciliation Recurring Basis Liability Gain Loss Includedin Earnings Net FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedinEarningsNet	32000000	USD
CY2018	mmc	Paymentof Contingent Consideration PaymentofContingentConsideration	36000000	USD
CY2020	us-gaap	Stock Issued1 StockIssued1	219000000	USD
CY2019	us-gaap	Stock Issued1 StockIssued1	165000000	USD
CY2018	us-gaap	Stock Issued1 StockIssued1	130000000	USD
CY2020	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	290000000	USD
CY2019	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	252000000	USD
CY2018	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	193000000	USD
CY2019Q1	us-gaap	Operating Lease Right Of Use Asset OperatingLeaseRightOfUseAsset	1700000000	USD
CY2020Q4	us-gaap	Allowance For Doubtful Accounts Receivable Current AllowanceForDoubtfulAccountsReceivableCurrent	142000000	USD
CY2019Q4	us-gaap	Allowance For Doubtful Accounts Receivable Current AllowanceForDoubtfulAccountsReceivableCurrent	140000000	USD
CY2018Q4	us-gaap	Allowance For Doubtful Accounts Receivable Current AllowanceForDoubtfulAccountsReceivableCurrent	112000000	USD
CY2019Q1	us-gaap	Operating Lease Liability Noncurrent OperatingLeaseLiabilityNoncurrent	1900000000	USD
CY2019Q4	us-gaap	Allowance For Doubtful Accounts Receivable Current AllowanceForDoubtfulAccountsReceivableCurrent	140000000	USD
CY2018Q4	us-gaap	Allowance For Doubtful Accounts Receivable Current AllowanceForDoubtfulAccountsReceivableCurrent	112000000	USD
CY2017Q4	us-gaap	Allowance For Doubtful Accounts Receivable Current AllowanceForDoubtfulAccountsReceivableCurrent	110000000	USD
CY2020	us-gaap	Provision For Doubtful Accounts ProvisionForDoubtfulAccounts	47000000	USD
CY2019	us-gaap	Provision For Doubtful Accounts ProvisionForDoubtfulAccounts	32000000	USD
CY2018	us-gaap	Provision For Doubtful Accounts ProvisionForDoubtfulAccounts	34000000	USD
CY2020	mmc	Allowance For Doubtful Accounts Receivable Writeoffs Net Of Recoveries AllowanceForDoubtfulAccountsReceivableWriteoffsNetOfRecoveries	30000000	USD
CY2019	mmc	Allowance For Doubtful Accounts Receivable Writeoffs Net Of Recoveries AllowanceForDoubtfulAccountsReceivableWriteoffsNetOfRecoveries	16000000	USD
CY2018	mmc	Allowance For Doubtful Accounts Receivable Writeoffs Net Of Recoveries AllowanceForDoubtfulAccountsReceivableWriteoffsNetOfRecoveries	24000000	USD
CY2020	mmc	Allowance For Doubtful Accounts Receivable Effect Of Exchange Rate Changes And Other AllowanceForDoubtfulAccountsReceivableEffectOfExchangeRateChangesAndOther	-15000000	USD
CY2019	mmc	Allowance For Doubtful Accounts Receivable Effect Of Exchange Rate Changes And Other AllowanceForDoubtfulAccountsReceivableEffectOfExchangeRateChangesAndOther	12000000	USD
CY2018	mmc	Allowance For Doubtful Accounts Receivable Effect Of Exchange Rate Changes And Other AllowanceForDoubtfulAccountsReceivableEffectOfExchangeRateChangesAndOther	-8000000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Before Reclassifications Net Of Tax OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax	-180000000	USD
CY2020	us-gaap	Reclassification From Accumulated Other Comprehensive Income Current Period Net Of Tax ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax	-125000000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	-55000000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Before Reclassifications Net Of Tax OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax	-492000000	USD
CY2019	us-gaap	Reclassification From Accumulated Other Comprehensive Income Current Period Net Of Tax ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax	-84000000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	-408000000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Foreign Currency Transaction And Translation Adjustment Before Tax OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentBeforeTax	559000000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Foreign Currency Translation Adjustment Tax OtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentTax	0	USD
CY2020	us-gaap	Other Comprehensive Income Loss Foreign Currency Transaction And Translation Adjustment Net Of Tax OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax	559000000	USD
CY2020	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	-2000000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Prior Service Cost Credit Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditTax	-1000000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Prior Service Cost Credit Net Of Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditNetOfTax	-1000000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax	-161000000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossTax	-37000000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax	-124000000	USD
CY2020	mmc	Other Comprehensive Income Loss Finalizationof Pensionand Other Postretirement Benefit Plan Valuation Effectof Settlement Before Tax OtherComprehensiveIncomeLossFinalizationofPensionandOtherPostretirementBenefitPlanValuationEffectofSettlementBeforeTax	3000000	USD
CY2020	mmc	Other Comprehensive Income Loss Finalizationof Pensionand Other Postretirement Benefit Plan Valuation Effectof Settlement Tax OtherComprehensiveIncomeLossFinalizationofPensionandOtherPostretirementBenefitPlanValuationEffectofSettlementTax	1000000	USD
CY2020	mmc	Other Comprehensive Income Loss Finalizationof Pensionand Other Postretirement Benefit Plan Valuation Effectof Settlement Netof Tax OtherComprehensiveIncomeLossFinalizationofPensionandOtherPostretirementBenefitPlanValuationEffectofSettlementNetofTax	2000000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansBeforeTax	162000000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansTax	37000000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansNetOfTax	125000000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Net Unamortized Gain Loss Arising During Period Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax	-772000000	USD
CY2020	us-gaap	Other Comprehensive Income Defined Benefit Plans Net Unamortized Gain Loss Arising During Period Tax OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodTax	-177000000	USD
CY2020	us-gaap	Other Comprehensive Income Defined Benefit Plans Net Unamortized Gain Loss Arising During Period Net Of Tax OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax	-595000000	USD
CY2020	mmc	Other Comprehensive Income Loss Pensionand Other Postretirement Benefit Plans Foreign Currency Transactionand Translation Adjustment Before Tax OtherComprehensiveIncomeLossPensionandOtherPostretirementBenefitPlansForeignCurrencyTransactionandTranslationAdjustmentBeforeTax	-163000000	USD
CY2020	mmc	Other Comprehensive Income Loss Pensionand Other Postretirement Benefit Plans Foreign Currency Transactionand Translation Adjustment Tax OtherComprehensiveIncomeLossPensionandOtherPostretirementBenefitPlansForeignCurrencyTransactionandTranslationAdjustmentTax	-28000000	USD
CY2020	mmc	Other Comprehensive Income Loss Pensionand Other Postretirement Benefit Plans Foreign Currency Transactionand Translation Adjustment Netof Tax OtherComprehensiveIncomeLossPensionandOtherPostretirementBenefitPlansForeignCurrencyTransactionandTranslationAdjustmentNetofTax	-135000000	USD
CY2020	mmc	Other Comprehensive Income Loss Adjustment From Mergerof Pension Plans Pensionand Postretirement Benefit Plans Before Tax OtherComprehensiveIncomeLossAdjustmentFromMergerofPensionPlansPensionandPostretirementBenefitPlansBeforeTax	-11000000	USD
CY2020	mmc	Other Comprehensive Income Loss Adjustment From Mergerof Pension Plans Pensionand Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossAdjustmentFromMergerofPensionPlansPensionandOtherPostretirementBenefitPlansTax	-2000000	USD
CY2020	mmc	Other Comprehensive Income Loss Adjustment From Mergerof Pension Plans Pensionand Other Postretirement Benefit Plans Netof Tax OtherComprehensiveIncomeLossAdjustmentFromMergerofPensionPlansPensionandOtherPostretirementBenefitPlansNetofTax	-9000000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax	784000000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax	170000000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	614000000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Before Tax OtherComprehensiveIncomeLossBeforeTax	-225000000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Tax OtherComprehensiveIncomeLossTax	-170000000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	-55000000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Foreign Currency Transaction And Translation Adjustment Before Tax OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentBeforeTax	148000000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Foreign Currency Translation Adjustment Tax OtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentTax	-3000000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Foreign Currency Transaction And Translation Adjustment Net Of Tax OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax	151000000	USD
CY2019	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	-2000000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Prior Service Cost Credit Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditTax	-1000000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Prior Service Cost Credit Net Of Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditNetOfTax	-1000000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax	-102000000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossTax	-22000000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax	-80000000	USD
CY2019	mmc	Other Comprehensive Income Loss Finalizationof Pensionand Other Postretirement Benefit Plan Valuation Effectof Settlement Before Tax OtherComprehensiveIncomeLossFinalizationofPensionandOtherPostretirementBenefitPlanValuationEffectofSettlementBeforeTax	6000000	USD
CY2019	mmc	Other Comprehensive Income Loss Finalizationof Pensionand Other Postretirement Benefit Plan Valuation Effectof Settlement Tax OtherComprehensiveIncomeLossFinalizationofPensionandOtherPostretirementBenefitPlanValuationEffectofSettlementTax	1000000	USD
CY2019	mmc	Other Comprehensive Income Loss Finalizationof Pensionand Other Postretirement Benefit Plan Valuation Effectof Settlement Netof Tax OtherComprehensiveIncomeLossFinalizationofPensionandOtherPostretirementBenefitPlanValuationEffectofSettlementNetofTax	5000000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansBeforeTax	106000000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansTax	22000000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansNetOfTax	84000000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Net Unamortized Gain Loss Arising During Period Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax	-758000000	USD
CY2019	us-gaap	Other Comprehensive Income Defined Benefit Plans Net Unamortized Gain Loss Arising During Period Tax OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodTax	-154000000	USD
CY2019	us-gaap	Other Comprehensive Income Defined Benefit Plans Net Unamortized Gain Loss Arising During Period Net Of Tax OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax	-604000000	USD
CY2019	mmc	Other Comprehensive Income Loss Pensionand Other Postretirement Benefit Plans Foreign Currency Transactionand Translation Adjustment Before Tax OtherComprehensiveIncomeLossPensionandOtherPostretirementBenefitPlansForeignCurrencyTransactionandTranslationAdjustmentBeforeTax	-50000000	USD
CY2019	mmc	Other Comprehensive Income Loss Pensionand Other Postretirement Benefit Plans Foreign Currency Transactionand Translation Adjustment Tax OtherComprehensiveIncomeLossPensionandOtherPostretirementBenefitPlansForeignCurrencyTransactionandTranslationAdjustmentTax	-11000000	USD
CY2019	mmc	Other Comprehensive Income Loss Pensionand Other Postretirement Benefit Plans Foreign Currency Transactionand Translation Adjustment Netof Tax OtherComprehensiveIncomeLossPensionandOtherPostretirementBenefitPlansForeignCurrencyTransactionandTranslationAdjustmentNetofTax	-39000000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax	702000000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax	143000000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	559000000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Before Tax OtherComprehensiveIncomeLossBeforeTax	-554000000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Tax OtherComprehensiveIncomeLossTax	-146000000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	-408000000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Foreign Currency Transaction And Translation Adjustment Before Tax OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentBeforeTax	-529000000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Foreign Currency Translation Adjustment Tax OtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentTax	0	USD
CY2018	us-gaap	Other Comprehensive Income Loss Foreign Currency Transaction And Translation Adjustment Net Of Tax OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax	-529000000	USD
CY2018	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	-4000000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Prior Service Cost Credit Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditTax	-1000000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Prior Service Cost Credit Net Of Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditNetOfTax	-3000000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax	-145000000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossTax	-32000000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax	-113000000	USD
CY2018	mmc	Other Comprehensive Income Loss Finalizationof Pensionand Other Postretirement Benefit Plan Valuation Effectof Settlement Before Tax OtherComprehensiveIncomeLossFinalizationofPensionandOtherPostretirementBenefitPlanValuationEffectofSettlementBeforeTax	42000000	USD
CY2018	mmc	Other Comprehensive Income Loss Finalizationof Pensionand Other Postretirement Benefit Plan Valuation Effectof Settlement Tax OtherComprehensiveIncomeLossFinalizationofPensionandOtherPostretirementBenefitPlanValuationEffectofSettlementTax	8000000	USD
CY2018	mmc	Other Comprehensive Income Loss Finalizationof Pensionand Other Postretirement Benefit Plan Valuation Effectof Settlement Netof Tax OtherComprehensiveIncomeLossFinalizationofPensionandOtherPostretirementBenefitPlanValuationEffectofSettlementNetofTax	34000000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansBeforeTax	183000000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansTax	39000000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansNetOfTax	144000000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Net Unamortized Gain Loss Arising During Period Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax	-374000000	USD
CY2018	us-gaap	Other Comprehensive Income Defined Benefit Plans Net Unamortized Gain Loss Arising During Period Tax OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodTax	-88000000	USD
CY2018	us-gaap	Other Comprehensive Income Defined Benefit Plans Net Unamortized Gain Loss Arising During Period Net Of Tax OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax	-286000000	USD
CY2018	us-gaap	Business Acquisition Pro Forma Earnings Per Share Basic BusinessAcquisitionProFormaEarningsPerShareBasic	2.58
CY2018	mmc	Other Comprehensive Income Loss Pensionand Other Postretirement Benefit Plans Foreign Currency Transactionand Translation Adjustment Before Tax OtherComprehensiveIncomeLossPensionandOtherPostretirementBenefitPlansForeignCurrencyTransactionandTranslationAdjustmentBeforeTax	141000000	USD
CY2018	mmc	Other Comprehensive Income Loss Pensionand Other Postretirement Benefit Plans Foreign Currency Transactionand Translation Adjustment Tax OtherComprehensiveIncomeLossPensionandOtherPostretirementBenefitPlansForeignCurrencyTransactionandTranslationAdjustmentTax	25000000	USD
CY2018	mmc	Other Comprehensive Income Loss Pensionand Other Postretirement Benefit Plans Foreign Currency Transactionand Translation Adjustment Netof Tax OtherComprehensiveIncomeLossPensionandOtherPostretirementBenefitPlansForeignCurrencyTransactionandTranslationAdjustmentNetofTax	116000000	USD
CY2018	mmc	Other Comprehensive Income Loss Adjustment From Mergerof Pension Plans Pensionand Postretirement Benefit Plans Before Tax OtherComprehensiveIncomeLossAdjustmentFromMergerofPensionPlansPensionandPostretirementBenefitPlansBeforeTax	-41000000	USD
CY2018	mmc	Other Comprehensive Income Loss Adjustment From Mergerof Pension Plans Pensionand Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossAdjustmentFromMergerofPensionPlansPensionandOtherPostretirementBenefitPlansTax	-6000000	USD
CY2018	mmc	Other Comprehensive Income Loss Adjustment From Mergerof Pension Plans Pensionand Other Postretirement Benefit Plans Netof Tax OtherComprehensiveIncomeLossAdjustmentFromMergerofPensionPlansPensionandOtherPostretirementBenefitPlansNetofTax	-35000000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax	91000000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax	30000000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	61000000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Before Tax OtherComprehensiveIncomeLossBeforeTax	-620000000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Tax OtherComprehensiveIncomeLossTax	-30000000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	-590000000	USD
CY2020Q4	mmc	Accumulated Other Comprehensive Income Loss Foreign Currency Translation Adjustment Tax AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentTax	11000000	USD
CY2019Q4	mmc	Accumulated Other Comprehensive Income Loss Foreign Currency Translation Adjustment Tax AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentTax	14000000	USD
CY2020Q4	mmc	Accumulated Other Comprehensive Income Loss Defined Benefit Pension And Other Postretirement Plans Adjustment Tax AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansAdjustmentTax	1805000000	USD
CY2019Q4	mmc	Accumulated Other Comprehensive Income Loss Defined Benefit Pension And Other Postretirement Plans Adjustment Tax AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansAdjustmentTax	1635000000	USD
CY2020	us-gaap	Business Combination Consideration Transferred1 BusinessCombinationConsiderationTransferred1	877000000	USD
CY2020	us-gaap	Payments To Acquire Businesses Gross PaymentsToAcquireBusinessesGross	694000000	USD
CY2020	mmc	Business Combination Contingentand Deferred Consideration BusinessCombinationContingentandDeferredConsideration	183000000	USD
CY2020	us-gaap	Finitelived Intangible Assets Acquired1 FinitelivedIntangibleAssetsAcquired1	278000000	USD
CY2020	us-gaap	Business Combination Pro Forma Information Revenue Of Acquiree Since Acquisition Date Actual BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual	169000000	USD
CY2020	us-gaap	Business Combination Pro Forma Information Earnings Or Loss Of Acquiree Since Acquisition Date Actual BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual	11000000	USD
CY2019	us-gaap	Business Combination Pro Forma Information Revenue Of Acquiree Since Acquisition Date Actual BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual	1200000000	USD
CY2019	us-gaap	Business Combination Pro Forma Information Earnings Or Loss Of Acquiree Since Acquisition Date Actual BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual	-40000000	USD
CY2018	us-gaap	Business Combination Pro Forma Information Revenue Of Acquiree Since Acquisition Date Actual BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual	120000000	USD
CY2018	us-gaap	Business Combination Pro Forma Information Earnings Or Loss Of Acquiree Since Acquisition Date Actual BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual	2000000	USD
CY2020	us-gaap	Business Combination Acquisition Related Costs BusinessCombinationAcquisitionRelatedCosts	3000000	USD
CY2018	us-gaap	Business Combination Acquisition Related Costs BusinessCombinationAcquisitionRelatedCosts	7000000	USD
CY2019	us-gaap	Business Combination Consideration Transferred1 BusinessCombinationConsiderationTransferred1	5927000000	USD
CY2019	us-gaap	Payments To Acquire Businesses Gross PaymentsToAcquireBusinessesGross	5861000000	USD
CY2019	mmc	Business Combination Contingentand Deferred Consideration BusinessCombinationContingentandDeferredConsideration	66000000	USD
CY2020	us-gaap	Business Acquisitions Pro Forma Revenue BusinessAcquisitionsProFormaRevenue	17301000000	USD
CY2019	us-gaap	Business Acquisitions Pro Forma Revenue BusinessAcquisitionsProFormaRevenue	17323000000	USD
CY2018	us-gaap	Business Acquisitions Pro Forma Revenue BusinessAcquisitionsProFormaRevenue	17106000000	USD
CY2020	us-gaap	Business Acquisitions Pro Forma Net Income Loss BusinessAcquisitionsProFormaNetIncomeLoss	2021000000	USD
CY2019	us-gaap	Business Acquisitions Pro Forma Net Income Loss BusinessAcquisitionsProFormaNetIncomeLoss	1877000000	USD
CY2018	us-gaap	Business Acquisitions Pro Forma Net Income Loss BusinessAcquisitionsProFormaNetIncomeLoss	1302000000	USD
CY2020	us-gaap	Business Acquisition Pro Forma Earnings Per Share Basic BusinessAcquisitionProFormaEarningsPerShareBasic	3.99
CY2019	us-gaap	Business Acquisition Pro Forma Earnings Per Share Basic BusinessAcquisitionProFormaEarningsPerShareBasic	3.71
CY2020Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Two FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo	327000000	USD
CY2020	us-gaap	Business Acquisition Pro Forma Earnings Per Share Diluted BusinessAcquisitionProFormaEarningsPerShareDiluted	3.95
CY2019	us-gaap	Business Acquisition Pro Forma Earnings Per Share Diluted BusinessAcquisitionProFormaEarningsPerShareDiluted	3.67
CY2018	us-gaap	Business Acquisition Pro Forma Earnings Per Share Diluted BusinessAcquisitionProFormaEarningsPerShareDiluted	2.55
CY2019	mmc	Business Acquisition Pro Forma Acquisition Related Costs BusinessAcquisitionProFormaAcquisitionRelatedCosts	207000000	USD
CY2019Q4	us-gaap	Goodwill Goodwill	14671000000	USD
CY2018Q4	us-gaap	Goodwill Goodwill	9599000000	USD
CY2020	us-gaap	Goodwill Acquired During Period GoodwillAcquiredDuringPeriod	593000000	USD
CY2019	us-gaap	Goodwill Acquired During Period GoodwillAcquiredDuringPeriod	5124000000	USD
CY2020	us-gaap	Goodwill Other Increase Decrease GoodwillOtherIncreaseDecrease	253000000	USD
CY2019	us-gaap	Goodwill Other Increase Decrease GoodwillOtherIncreaseDecrease	-52000000	USD
CY2020Q4	us-gaap	Goodwill Goodwill	15517000000	USD
CY2019Q4	us-gaap	Goodwill Goodwill	14671000000	USD
CY2020Q4	us-gaap	Business Acquisition Purchase Price Allocation Goodwill Expected Tax Deductible Amount BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount	179000000	USD
CY2019	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	70000000	USD
CY2019Q4	us-gaap	Business Acquisition Purchase Price Allocation Goodwill Expected Tax Deductible Amount BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount	213000000	USD
CY2020Q4	us-gaap	Finite Lived Intangible Assets Gross FiniteLivedIntangibleAssetsGross	4099000000	USD
CY2020Q4	us-gaap	Finite Lived Intangible Assets Accumulated Amortization FiniteLivedIntangibleAssetsAccumulatedAmortization	1400000000	USD
CY2020Q4	us-gaap	Finite Lived Intangible Assets Net FiniteLivedIntangibleAssetsNet	2699000000	USD
CY2019Q4	us-gaap	Finite Lived Intangible Assets Gross FiniteLivedIntangibleAssetsGross	3874000000	USD
CY2019Q4	us-gaap	Finite Lived Intangible Assets Accumulated Amortization FiniteLivedIntangibleAssetsAccumulatedAmortization	1100000000	USD
CY2019Q4	us-gaap	Finite Lived Intangible Assets Net FiniteLivedIntangibleAssetsNet	2774000000	USD
CY2020	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	351000000	USD
CY2019	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	314000000	USD
CY2018	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	183000000	USD
CY2020Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Next Twelve Months FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths	356000000	USD
CY2018	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	82000000	USD
CY2020	us-gaap	Current Foreign Tax Expense Benefit CurrentForeignTaxExpenseBenefit	456000000	USD
CY2020Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Three FiniteLivedIntangibleAssetsAmortizationExpenseYearThree	300000000	USD
CY2020Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Four FiniteLivedIntangibleAssetsAmortizationExpenseYearFour	285000000	USD
CY2020Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Five FiniteLivedIntangibleAssetsAmortizationExpenseYearFive	275000000	USD
CY2020Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense After Year Five FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive	1156000000	USD
CY2020Q4	us-gaap	Finite Lived Intangible Assets Net FiniteLivedIntangibleAssetsNet	2699000000	USD
CY2020	us-gaap	Income Loss From Continuing Operations Before Income Taxes Domestic IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic	1075000000	USD
CY2019	us-gaap	Income Loss From Continuing Operations Before Income Taxes Domestic IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic	657000000	USD
CY2018	us-gaap	Income Loss From Continuing Operations Before Income Taxes Domestic IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic	460000000	USD
CY2020	us-gaap	Income Loss From Continuing Operations Before Income Taxes Foreign IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign	1718000000	USD
CY2019	us-gaap	Income Loss From Continuing Operations Before Income Taxes Foreign IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign	1782000000	USD
CY2018	us-gaap	Income Loss From Continuing Operations Before Income Taxes Foreign IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign	1784000000	USD
CY2020	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	2793000000	USD
CY2019	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	2439000000	USD
CY2018	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	2244000000	USD
CY2020	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	172000000	USD
CY2019	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	57000000	USD
CY2019	us-gaap	Current Foreign Tax Expense Benefit CurrentForeignTaxExpenseBenefit	455000000	USD
CY2018	us-gaap	Current Foreign Tax Expense Benefit CurrentForeignTaxExpenseBenefit	449000000	USD
CY2020	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	79000000	USD
CY2018	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	82000000	USD
CY2020	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	707000000	USD
CY2019	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	582000000	USD
CY2018	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	613000000	USD
CY2020	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	40000000	USD
CY2019	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	69000000	USD
CY2018	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	-30000000	USD
CY2020	us-gaap	Deferred Foreign Income Tax Expense Benefit DeferredForeignIncomeTaxExpenseBenefit	-14000000	USD
CY2019	us-gaap	Deferred Foreign Income Tax Expense Benefit DeferredForeignIncomeTaxExpenseBenefit	-16000000	USD
CY2018	us-gaap	Deferred Foreign Income Tax Expense Benefit DeferredForeignIncomeTaxExpenseBenefit	-1000000	USD
CY2020	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	14000000	USD
CY2019	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	31000000	USD
CY2018	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	-8000000	USD
CY2020	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	40000000	USD
CY2019	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	84000000	USD
CY2018	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	-39000000	USD
CY2020	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	747000000	USD
CY2019	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	666000000	USD
CY2018	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	574000000	USD
CY2020Q4	mmc	Deferred Tax Assets Tax Deferred Expense Reservesand Accruals Netof Valuation Allowance DeferredTaxAssetsTaxDeferredExpenseReservesandAccrualsNetofValuationAllowance	547000000	USD
CY2019Q4	mmc	Deferred Tax Assets Tax Deferred Expense Reservesand Accruals Netof Valuation Allowance DeferredTaxAssetsTaxDeferredExpenseReservesandAccrualsNetofValuationAllowance	492000000	USD
CY2020Q4	mmc	Deferred Tax Assets Operating Loss Carryforwards Foreign Netof Valuation Allowance DeferredTaxAssetsOperatingLossCarryforwardsForeignNetofValuationAllowance	294000000	USD
CY2019Q4	mmc	Deferred Tax Assets Operating Loss Carryforwards Foreign Netof Valuation Allowance DeferredTaxAssetsOperatingLossCarryforwardsForeignNetofValuationAllowance	324000000	USD
CY2020Q4	mmc	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Pensions And Postretirement Benefits Netof Valuation Allowance DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPensionsAndPostretirementBenefitsNetofValuationAllowance	494000000	USD
CY2019Q4	mmc	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Pensions And Postretirement Benefits Netof Valuation Allowance DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPensionsAndPostretirementBenefitsNetofValuationAllowance	438000000	USD
CY2020Q4	mmc	Deferred Tax Assets Operating Loss Carryforwards Domestic Net Of Valuation Allowance DeferredTaxAssetsOperatingLossCarryforwardsDomesticNetOfValuationAllowance	60000000	USD
CY2019Q4	mmc	Deferred Tax Assets Operating Loss Carryforwards Domestic Net Of Valuation Allowance DeferredTaxAssetsOperatingLossCarryforwardsDomesticNetOfValuationAllowance	70000000	USD
CY2020Q4	mmc	Deferred Tax Assets Deferred Income Net Of Valuation Allowance DeferredTaxAssetsDeferredIncomeNetOfValuationAllowance	25000000	USD
CY2019Q4	mmc	Deferred Tax Assets Deferred Income Net Of Valuation Allowance DeferredTaxAssetsDeferredIncomeNetOfValuationAllowance	19000000	USD
CY2020Q4	mmc	Deferred Tax Assets Tax Deferred Expense Other Net Of Valuation Allowance DeferredTaxAssetsTaxDeferredExpenseOtherNetOfValuationAllowance	43000000	USD
CY2019Q4	mmc	Deferred Tax Assets Tax Deferred Expense Other Net Of Valuation Allowance DeferredTaxAssetsTaxDeferredExpenseOtherNetOfValuationAllowance	27000000	USD
CY2020Q4	mmc	Deferred Tax Assets Net Net Of Valuation Allowance DeferredTaxAssetsNetNetOfValuationAllowance	1463000000	USD
CY2019Q4	mmc	Deferred Tax Assets Net Net Of Valuation Allowance DeferredTaxAssetsNetNetOfValuationAllowance	1370000000	USD
CY2020Q4	us-gaap	Deferred Tax Liabilities Undistributed Foreign Earnings DeferredTaxLiabilitiesUndistributedForeignEarnings	569000000	USD
CY2019Q4	us-gaap	Deferred Tax Liabilities Undistributed Foreign Earnings DeferredTaxLiabilitiesUndistributedForeignEarnings	400000000	USD
CY2020Q4	us-gaap	Deferred Tax Liabilities Property Plant And Equipment DeferredTaxLiabilitiesPropertyPlantAndEquipment	491000000	USD
CY2019Q4	us-gaap	Deferred Tax Liabilities Property Plant And Equipment DeferredTaxLiabilitiesPropertyPlantAndEquipment	594000000	USD
CY2020Q4	us-gaap	Deferred Tax Liabilities Deferred Expense Reserves And Accruals DeferredTaxLiabilitiesDeferredExpenseReservesAndAccruals	143000000	USD
CY2019Q4	us-gaap	Deferred Tax Liabilities Deferred Expense Reserves And Accruals DeferredTaxLiabilitiesDeferredExpenseReservesAndAccruals	151000000	USD
CY2020Q4	us-gaap	Deferred Tax Liabilities Deferred Expense DeferredTaxLiabilitiesDeferredExpense	87000000	USD
CY2019Q4	us-gaap	Deferred Tax Liabilities Deferred Expense DeferredTaxLiabilitiesDeferredExpense	77000000	USD
CY2020Q4	us-gaap	Deferred Tax Liabilities Other DeferredTaxLiabilitiesOther	32000000	USD
CY2019Q4	us-gaap	Deferred Tax Liabilities Other DeferredTaxLiabilitiesOther	37000000	USD
CY2020Q4	us-gaap	Deferred Income Tax Liabilities DeferredIncomeTaxLiabilities	1322000000	USD
CY2019Q4	us-gaap	Deferred Income Tax Liabilities DeferredIncomeTaxLiabilities	1259000000	USD
CY2020Q4	us-gaap	Undistributed Earnings Of Foreign Subsidiaries UndistributedEarningsOfForeignSubsidiaries	700000000	USD
CY2020	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.210
CY2019	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.210
CY2018	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.210
CY2020	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0.025
CY2019	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0.030
CY2018	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0.023
CY2020	us-gaap	Effective Income Tax Rate Reconciliation Foreign Income Tax Rate Differential EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential	0.023
CY2019	us-gaap	Effective Income Tax Rate Reconciliation Foreign Income Tax Rate Differential EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential	0.030
CY2018	us-gaap	Effective Income Tax Rate Reconciliation Foreign Income Tax Rate Differential EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential	0.033
CY2020	mmc	Effective Income Tax Rate Reconciliation Tax Reform Percent EffectiveIncomeTaxRateReconciliationTaxReformPercent	0
CY2019	mmc	Effective Income Tax Rate Reconciliation Tax Reform Percent EffectiveIncomeTaxRateReconciliationTaxReformPercent	0
CY2018	mmc	Effective Income Tax Rate Reconciliation Tax Reform Percent EffectiveIncomeTaxRateReconciliationTaxReformPercent	-0.003
CY2020	us-gaap	Effective Income Tax Rate Reconciliation Nondeductible Expense Share Based Compensation Cost EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost	-0.014
CY2019	us-gaap	Effective Income Tax Rate Reconciliation Nondeductible Expense Share Based Compensation Cost EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost	-0.013
CY2018	us-gaap	Effective Income Tax Rate Reconciliation Nondeductible Expense Share Based Compensation Cost EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost	-0.010
CY2020	us-gaap	Effective Income Tax Rate Reconciliation Tax Contingencies EffectiveIncomeTaxRateReconciliationTaxContingencies	0.011
CY2019	us-gaap	Effective Income Tax Rate Reconciliation Tax Contingencies EffectiveIncomeTaxRateReconciliationTaxContingencies	0
CY2018	us-gaap	Effective Income Tax Rate Reconciliation Tax Contingencies EffectiveIncomeTaxRateReconciliationTaxContingencies	0
CY2020	us-gaap	Effective Income Tax Rate Reconciliation Other Adjustments EffectiveIncomeTaxRateReconciliationOtherAdjustments	0.012
CY2019	us-gaap	Effective Income Tax Rate Reconciliation Other Adjustments EffectiveIncomeTaxRateReconciliationOtherAdjustments	0.016
CY2018	us-gaap	Effective Income Tax Rate Reconciliation Other Adjustments EffectiveIncomeTaxRateReconciliationOtherAdjustments	0.003
CY2020	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0.267
CY2019	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0.273
CY2018	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0.256
CY2020	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0.267
CY2019	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0.273
CY2018	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0.256
CY2020	us-gaap	Valuation Allowance Deferred Tax Asset Change In Amount ValuationAllowanceDeferredTaxAssetChangeInAmount	72000000	USD
CY2019	us-gaap	Valuation Allowance Deferred Tax Asset Change In Amount ValuationAllowanceDeferredTaxAssetChangeInAmount	60000000	USD
CY2018	us-gaap	Valuation Allowance Deferred Tax Asset Change In Amount ValuationAllowanceDeferredTaxAssetChangeInAmount	36000000	USD
CY2020	us-gaap	Income Tax Reconciliation Change In Deferred Tax Assets Valuation Allowance IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance	-14000000	USD
CY2019	us-gaap	Income Tax Reconciliation Change In Deferred Tax Assets Valuation Allowance IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance	0	USD
CY2018	us-gaap	Income Tax Reconciliation Change In Deferred Tax Assets Valuation Allowance IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance	1000000	USD
CY2020	mmc	Operating Loss Carryforwards Percentage Subjectto Expiration OperatingLossCarryforwardsPercentageSubjecttoExpiration	0.58
CY2019Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	86000000	USD
CY2018Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	78000000	USD
CY2017Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	71000000	USD
CY2020	us-gaap	Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions	9000000	USD
CY2019	us-gaap	Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions	8000000	USD
CY2018	us-gaap	Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions	6000000	USD
CY2020	us-gaap	Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions	25000000	USD
CY2019	us-gaap	Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions	15000000	USD
CY2018	us-gaap	Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions	6000000	USD
CY2020	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions	9000000	USD
CY2019	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions	1000000	USD
CY2018	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions	0	USD
CY2020	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Settlements With Taxing Authorities UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities	4000000	USD
CY2019	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Settlements With Taxing Authorities UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities	1000000	USD
CY2018	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Settlements With Taxing Authorities UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities	2000000	USD
CY2020	us-gaap	Unrecognized Tax Benefits Reductions Resulting From Lapse Of Applicable Statute Of Limitations UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations	9000000	USD
CY2019	us-gaap	Unrecognized Tax Benefits Reductions Resulting From Lapse Of Applicable Statute Of Limitations UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations	13000000	USD
CY2018	us-gaap	Unrecognized Tax Benefits Reductions Resulting From Lapse Of Applicable Statute Of Limitations UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations	3000000	USD
CY2020Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	98000000	USD
CY2019Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	86000000	USD
CY2018Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	78000000	USD
CY2020Q4	us-gaap	Unrecognized Tax Benefits That Would Impact Effective Tax Rate UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate	90000000	USD
CY2019Q4	us-gaap	Unrecognized Tax Benefits That Would Impact Effective Tax Rate UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate	75000000	USD
CY2018Q4	us-gaap	Unrecognized Tax Benefits That Would Impact Effective Tax Rate UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate	64000000	USD
CY2020Q4	us-gaap	Unrecognized Tax Benefits Income Tax Penalties And Interest Accrued UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued	40000000	USD
CY2019Q4	us-gaap	Unrecognized Tax Benefits Income Tax Penalties And Interest Accrued UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued	31000000	USD
CY2018Q4	us-gaap	Unrecognized Tax Benefits Income Tax Penalties And Interest Accrued UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued	15000000	USD
CY2020	mmc	Defined Benefit Plan Marketrelated Plan Assets Value Recognition Periodof Investment Gainsand Losses DefinedBenefitPlanMarketrelatedPlanAssetsValueRecognitionPeriodofInvestmentGainsandLosses	P5Y
CY2020	mmc	Defined Benefit Plan Marketrelated Plan Assets Value Recognition Periodof Investment Gainsand Losses DefinedBenefitPlanMarketrelatedPlanAssetsValueRecognitionPeriodofInvestmentGainsandLosses	P5Y
CY2020Q4	us-gaap	Defined Benefit Plan Health Care Cost Trend Rate Assumed Next Fiscal Year DefinedBenefitPlanHealthCareCostTrendRateAssumedNextFiscalYear	0.0493
CY2020Q4	us-gaap	Defined Benefit Plan Ultimate Health Care Cost Trend Rate1 DefinedBenefitPlanUltimateHealthCareCostTrendRate1	0.0422
CY2020Q4	us-gaap	Defined Benefit Plan Fair Value Of Plan Assets DefinedBenefitPlanFairValueOfPlanAssets	19074000000	USD
CY2017Q1	us-gaap	Defined Contribution Plan Employer Matching Contribution Percent DefinedContributionPlanEmployerMatchingContributionPercent	0.04
CY2020Q4	mmc	Defined Contribution Plan Employee Stock Ownership Plan Esop Sharesin Esop Value DefinedContributionPlanEmployeeStockOwnershipPlanESOPSharesinESOPValue	537000000	USD
CY2019Q4	mmc	Defined Contribution Plan Employee Stock Ownership Plan Esop Sharesin Esop Value DefinedContributionPlanEmployeeStockOwnershipPlanESOPSharesinESOPValue	556000000	USD
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Risk Free Interest Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate	0.0144
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Risk Free Interest Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate	0.0251
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Risk Free Interest Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate	0.0273
CY2020	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Fair Value Assumptions Expected Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1	P6Y
CY2019	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Fair Value Assumptions Expected Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1	P6Y
CY2018	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Fair Value Assumptions Expected Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1	P6Y
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Volatility Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate	0.2033
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Volatility Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate	0.2093
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Volatility Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate	0.2323
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Dividend Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate	0.0153
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Dividend Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate	0.0182
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Dividend Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate	0.0181
CY2019Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber	8859128	shares
CY2019Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice	64.69
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross	1326790	shares
CY2020	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Grants In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice	118.87
CY2020	us-gaap	Stock Issued During Period Shares Stock Options Exercised StockIssuedDuringPeriodSharesStockOptionsExercised	2348898	shares
CY2020	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Exercises In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice	44.72
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod	67125	shares
CY2020	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Forfeitures In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice	96.09
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber	7769895	shares
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice	79.71
CY2020	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Outstanding Weighted Average Remaining Contractual Term2 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2	P6Y6M
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue	285520000	USD
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Outstanding Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber	7645454	shares
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Outstanding Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice	79.45
CY2020	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Vested And Expected To Vest Outstanding Weighted Average Remaining Contractual Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1	P6Y6M
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Outstanding Aggregate Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue	282844000	USD
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber	4299859	shares
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice	64.71
CY2020	us-gaap	Sharebased Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Exercisable Options Weighted Average Remaining Contractual Term2 SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageRemainingContractualTerm2	P5Y2M12D
CY2020Q4	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Exercisable Intrinsic Value1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1	220402000	USD
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue	21.09
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue	17.87
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue	18.29
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercises In Period Total Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue	159300000	USD
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercises In Period Total Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue	136700000	USD
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercises In Period Total Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue	72900000	USD
CY2020	us-gaap	Proceeds From Stock Options Exercised ProceedsFromStockOptionsExercised	72000000.0	USD
CY2019	us-gaap	Proceeds From Stock Options Exercised ProceedsFromStockOptionsExercised	106500000	USD
CY2018	us-gaap	Proceeds From Stock Options Exercised ProceedsFromStockOptionsExercised	46700000	USD
CY2019Q4	us-gaap	Fair Value Measurement With Unobservable Inputs Reconciliations Recurring Basis Liability Value FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue	225000000	USD
CY2018Q4	us-gaap	Fair Value Measurement With Unobservable Inputs Reconciliations Recurring Basis Liability Value FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue	508000000	USD
CY2020	us-gaap	Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Liability Purchases FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases	107000000	USD
CY2019	us-gaap	Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Liability Purchases FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases	36000000	USD
CY2020	us-gaap	Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Liability Settlements FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements	102000000	USD
CY2019	us-gaap	Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Liability Settlements FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements	63000000	USD
CY2020	us-gaap	Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Liability Gain Loss Included In Earnings FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings	11000000	USD
CY2019	us-gaap	Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Liability Gain Loss Included In Earnings FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings	70000000	USD
CY2020	mmc	Fair Value Measurementwith Unobservable Inputs Reconciliation Recurring Basis Liability Other Adjustments FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisLiabilityOtherAdjustments	2000000	USD
CY2019	mmc	Fair Value Measurementwith Unobservable Inputs Reconciliation Recurring Basis Liability Other Adjustments FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisLiabilityOtherAdjustments	-1000000	USD
CY2020Q4	us-gaap	Fair Value Measurement With Unobservable Inputs Reconciliations Recurring Basis Liability Value FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue	243000000	USD
CY2019Q4	us-gaap	Fair Value Measurement With Unobservable Inputs Reconciliations Recurring Basis Liability Value FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue	225000000	USD
CY2020	us-gaap	Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Liability Gain Loss Included In Earnings FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings	11000000	USD
CY2020	mmc	Increasein Fair Valueof Contingent Consideration Dueto Five Percent Increasein Projections IncreaseinFairValueofContingentConsiderationDuetoFivePercentIncreaseinProjections	12000000	USD
CY2020	mmc	Decreasein Fair Valueof Contingent Consideration Dueto Five Percent Decreasein Projections DecreaseinFairValueofContingentConsiderationDuetoFivePercentDecreaseinProjections	21000000	USD
CY2020Q4	us-gaap	Equity Method Investments EquityMethodInvestments	280000000	USD
CY2019Q4	us-gaap	Equity Method Investments EquityMethodInvestments	434000000	USD
CY2020	us-gaap	Equity Securities Fv Ni Realized Gain Loss EquitySecuritiesFvNiRealizedGainLoss	-27000000	USD
CY2019	us-gaap	Equity Securities Fv Ni Realized Gain Loss EquitySecuritiesFvNiRealizedGainLoss	10000000	USD
CY2020Q4	us-gaap	Equity Securities Without Readily Determinable Fair Value Amount EquitySecuritiesWithoutReadilyDeterminableFairValueAmount	33000000	USD
CY2019Q4	us-gaap	Equity Securities Without Readily Determinable Fair Value Amount EquitySecuritiesWithoutReadilyDeterminableFairValueAmount	67000000	USD
CY2020	us-gaap	Other Comprehensive Income Foreign Currency Transaction And Translation Gain Loss Before Reclassification And Tax OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossBeforeReclassificationAndTax	-124000000	USD
CY2020	us-gaap	Operating Lease Impairment Loss OperatingLeaseImpairmentLoss	28000000	USD
CY2019	us-gaap	Operating Lease Impairment Loss OperatingLeaseImpairmentLoss	9000000	USD
CY2020	us-gaap	Operating Lease Cost OperatingLeaseCost	396000000	USD
CY2019	us-gaap	Operating Lease Cost OperatingLeaseCost	371000000	USD
CY2020	us-gaap	Short Term Lease Cost ShortTermLeaseCost	3000000	USD
CY2019	us-gaap	Short Term Lease Cost ShortTermLeaseCost	8000000	USD
CY2019Q4	us-gaap	Debt Current DebtCurrent	1215000000	USD
CY2020Q4	us-gaap	Long Term Debt LongTermDebt	11313000000	USD
CY2020	us-gaap	Variable Lease Cost VariableLeaseCost	138000000	USD
CY2019	us-gaap	Variable Lease Cost VariableLeaseCost	150000000	USD
CY2020	us-gaap	Sublease Income SubleaseIncome	19000000	USD
CY2019	us-gaap	Sublease Income SubleaseIncome	18000000	USD
CY2020	us-gaap	Lease Cost LeaseCost	518000000	USD
CY2019	us-gaap	Lease Cost LeaseCost	511000000	USD
CY2020	us-gaap	Operating Lease Payments OperatingLeasePayments	420000000	USD
CY2019	us-gaap	Operating Lease Payments OperatingLeasePayments	392000000	USD
CY2020	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	261000000	USD
CY2019	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	140000000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due Next Twelve Months LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths	410000000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Two LesseeOperatingLeaseLiabilityPaymentsDueYearTwo	380000000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Three LesseeOperatingLeaseLiabilityPaymentsDueYearThree	331000000	USD
CY2019	us-gaap	Restructuring Reserve Translation Adjustment RestructuringReserveTranslationAdjustment	-10000000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Four LesseeOperatingLeaseLiabilityPaymentsDueYearFour	288000000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Five LesseeOperatingLeaseLiabilityPaymentsDueYearFive	256000000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due After Year Five LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive	905000000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due LesseeOperatingLeaseLiabilityPaymentsDue	2570000000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Undiscounted Excess Amount LesseeOperatingLeaseLiabilityUndiscountedExcessAmount	304000000	USD
CY2020Q4	us-gaap	Operating Lease Liability OperatingLeaseLiability	2266000000	USD
CY2020Q4	us-gaap	Operating Lease Liability Current OperatingLeaseLiabilityCurrent	342000000	USD
CY2020Q4	us-gaap	Operating Lease Liability Noncurrent OperatingLeaseLiabilityNoncurrent	1924000000	USD
CY2020Q4	us-gaap	Operating Lease Liability OperatingLeaseLiability	2266000000	USD
CY2020Q4	mmc	Lessee Operating Lease Lease Notyet Commenced Amount LesseeOperatingLeaseLeaseNotyetCommencedAmount	3000000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Lease Not Yet Commenced Term Of Contract1 LesseeOperatingLeaseLeaseNotYetCommencedTermOfContract1	P12M
CY2018	us-gaap	Operating Leases Rent Expense Net OperatingLeasesRentExpenseNet	383000000	USD
CY2020Q4	us-gaap	Long Term Debt Current LongTermDebtCurrent	517000000	USD
CY2019Q4	us-gaap	Long Term Debt Current LongTermDebtCurrent	1215000000	USD
CY2020Q4	us-gaap	Debt Current DebtCurrent	517000000	USD
CY2019Q4	us-gaap	Long Term Debt LongTermDebt	11956000000	USD
CY2020Q4	us-gaap	Long Term Debt Current LongTermDebtCurrent	517000000	USD
CY2019Q4	us-gaap	Long Term Debt Current LongTermDebtCurrent	1215000000	USD
CY2020Q4	us-gaap	Long Term Debt Noncurrent LongTermDebtNoncurrent	10796000000	USD
CY2019Q4	us-gaap	Long Term Debt Noncurrent LongTermDebtNoncurrent	10741000000	USD
CY2020Q4	us-gaap	Commercial Paper CommercialPaper	0	USD
CY2020Q4	us-gaap	Long Term Debt Maturities Repayments Of Principal In Next Twelve Months LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths	517000000	USD
CY2020Q4	us-gaap	Long Term Debt Maturities Repayments Of Principal In Year Two LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo	516000000	USD
CY2020Q4	us-gaap	Long Term Debt Maturities Repayments Of Principal In Year Three LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree	619000000	USD
CY2020Q4	us-gaap	Long Term Debt Maturities Repayments Of Principal In Year Four LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour	1600000000	USD
CY2020Q4	us-gaap	Long Term Debt Maturities Repayments Of Principal In Year Five LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive	518000000	USD
CY2018Q4	us-gaap	Restructuring Reserve RestructuringReserve	112000000	USD
CY2019	us-gaap	Restructuring Charges RestructuringCharges	112000000	USD
CY2019	us-gaap	Payments For Restructuring PaymentsForRestructuring	112000000	USD
CY2019Q4	us-gaap	Restructuring Reserve RestructuringReserve	102000000	USD
CY2020	us-gaap	Restructuring Charges RestructuringCharges	89000000	USD
CY2020	us-gaap	Payments For Restructuring PaymentsForRestructuring	100000000	USD
CY2020	us-gaap	Restructuring Reserve Translation Adjustment RestructuringReserveTranslationAdjustment	-10000000	USD
CY2020Q4	us-gaap	Restructuring Reserve RestructuringReserve	81000000	USD
CY2019	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	485000000	USD
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Shares Issued In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod	4100000	shares
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Shares Issued In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod	4600000	shares
CY2020Q4	us-gaap	Loss Contingency Estimate Of Possible Loss LossContingencyEstimateOfPossibleLoss	155000000	GBP
CY2020Q4	us-gaap	Loss Contingency Estimate Of Possible Loss LossContingencyEstimateOfPossibleLoss	210000000	USD
CY2020	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	17224000000	USD
CY2020	us-gaap	Operating Income Loss OperatingIncomeLoss	3066000000	USD
CY2020Q4	us-gaap	Assets Assets	33049000000	USD
CY2020	us-gaap	Depreciation Depletion And Amortization DepreciationDepletionAndAmortization	741000000	USD
CY2020	us-gaap	Payments To Acquire Productive Assets PaymentsToAcquireProductiveAssets	348000000	USD
CY2019	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	16652000000	USD
CY2019	us-gaap	Operating Income Loss OperatingIncomeLoss	2677000000	USD
CY2019Q4	us-gaap	Assets Assets	31357000000	USD
CY2019	us-gaap	Depreciation Depletion And Amortization DepreciationDepletionAndAmortization	647000000	USD
CY2019	us-gaap	Payments To Acquire Productive Assets PaymentsToAcquireProductiveAssets	421000000	USD
CY2018	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	14950000000	USD
CY2018	us-gaap	Operating Income Loss OperatingIncomeLoss	2761000000	USD
CY2018Q4	us-gaap	Assets Assets	21578000000	USD
CY2018	us-gaap	Depreciation Depletion And Amortization DepreciationDepletionAndAmortization	494000000	USD
CY2018	us-gaap	Payments To Acquire Productive Assets PaymentsToAcquireProductiveAssets	314000000	USD
CY2020Q2	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	1.13
CY2020Q3	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.62
CY2020	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	17224000000	USD
CY2019	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	16652000000	USD
CY2018	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	14950000000	USD
CY2020	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	17224000000	USD
CY2019	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	16652000000	USD
CY2018	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	14950000000	USD
CY2020Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	856000000	USD
CY2019Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	858000000	USD
CY2018Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	701000000	USD
CY2020Q1	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	4651000000	USD
CY2020Q2	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	4189000000	USD
CY2020Q3	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	3968000000	USD
CY2020Q4	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	4416000000	USD
CY2020Q1	us-gaap	Operating Income Loss OperatingIncomeLoss	1070000000	USD
CY2020Q2	us-gaap	Operating Income Loss OperatingIncomeLoss	885000000	USD
CY2020Q3	us-gaap	Operating Income Loss OperatingIncomeLoss	540000000	USD
CY2020Q4	us-gaap	Operating Income Loss OperatingIncomeLoss	571000000	USD
CY2020Q1	us-gaap	Profit Loss ProfitLoss	767000000	USD
CY2020Q2	us-gaap	Profit Loss ProfitLoss	580000000	USD
CY2020Q3	us-gaap	Profit Loss ProfitLoss	320000000	USD
CY2020Q4	us-gaap	Profit Loss ProfitLoss	379000000	USD
CY2020Q1	us-gaap	Net Income Loss NetIncomeLoss	754000000	USD
CY2020Q2	us-gaap	Net Income Loss NetIncomeLoss	572000000	USD
CY2020Q3	us-gaap	Net Income Loss NetIncomeLoss	316000000	USD
CY2020Q4	us-gaap	Net Income Loss NetIncomeLoss	374000000	USD
CY2020Q1	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	1.49
CY2019Q4	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.76
CY2019Q1	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	0.415
CY2019Q2	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	0.415
CY2019Q3	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	0.455
CY2020Q4	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.74
CY2020Q1	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	1.48
CY2020Q2	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	1.12
CY2020Q3	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.62
CY2020Q4	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.73
CY2020Q1	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	0.455
CY2020Q2	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	0.455
CY2020Q3	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	0.465
CY2020Q4	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	0.465
CY2019Q1	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	4071000000	USD
CY2019Q2	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	4349000000	USD
CY2019Q3	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	3968000000	USD
CY2019Q4	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	4264000000	USD
CY2019Q1	us-gaap	Operating Income Loss OperatingIncomeLoss	938000000	USD
CY2019Q2	us-gaap	Operating Income Loss OperatingIncomeLoss	680000000	USD
CY2019Q3	us-gaap	Operating Income Loss OperatingIncomeLoss	467000000	USD
CY2019Q4	us-gaap	Operating Income Loss OperatingIncomeLoss	592000000	USD
CY2019Q1	us-gaap	Profit Loss ProfitLoss	727000000	USD
CY2019Q2	us-gaap	Profit Loss ProfitLoss	344000000	USD
CY2019Q3	us-gaap	Profit Loss ProfitLoss	306000000	USD
CY2019Q4	us-gaap	Profit Loss ProfitLoss	396000000	USD
CY2019Q1	us-gaap	Net Income Loss NetIncomeLoss	716000000	USD
CY2019Q2	us-gaap	Net Income Loss NetIncomeLoss	332000000	USD
CY2019Q3	us-gaap	Net Income Loss NetIncomeLoss	303000000	USD
CY2019Q4	us-gaap	Net Income Loss NetIncomeLoss	391000000	USD
CY2019Q1	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	1.42
CY2019Q2	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.66
CY2019Q3	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.60
CY2019Q4	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.77
CY2019Q1	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	1.40
CY2019Q2	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.65
CY2019Q3	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.59
CY2019Q4	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	0.455

Files In Submission

Name	View Source	Status
0000062709-21-000008-index-headers.html	Edgar Link	pending
0000062709-21-000008-index.html	Edgar Link	pending
0000062709-21-000008.txt	Edgar Link	pending
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FilingSummary.xml	Edgar Link	unprocessable
Financial_Report.xlsx	Edgar Link	pending
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mmc-20201231.htm	Edgar Link	pending
mmc-20201231.xsd	Edgar Link	pending
mmc-20201231_cal.xml	Edgar Link	unprocessable
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mmc-20201231_htm.xml	Edgar Link	completed
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mmc-20201231_pre.xml	Edgar Link	unprocessable
mmc12312020ex_1062.htm	Edgar Link	pending
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$MMC
MARSH & MCLENNAN COMPANIES, INC. Stock $mmc

2020 Q4 Form 10-K Financial Statement

#000006270921000008 Filed on February 17, 2021

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$MMC MARSH & MCLENNAN COMPANIES, INC. Stock $mmc

2020 Q4 Form 10-K Financial Statement

#000006270921000008 Filed on February 17, 2021

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$MMC
MARSH & MCLENNAN COMPANIES, INC. Stock $mmc