$WAL
WESTERN ALLIANCE BANCORPORATION Stock $wal

$wal Overview Financials Valuation SEC Filings Company Website

2021 Q4 Form 10-K Financial Statement

#000121254522000090 Filed on February 25, 2022

Income Statement

Concept	2021 Q4	2021	2020 Q4
Revenue		$1.659B	$331.6M
YoY Change		31.46%	5.14%
Cost Of Revenue
YoY Change
Gross Profit
YoY Change
Gross Profit Margin
Selling, General & Admin
YoY Change
% of Gross Profit
Research & Development
YoY Change
% of Gross Profit
Depreciation & Amortization	$8.100M	$20.70M	$5.800M
YoY Change	39.66%	36.18%	16.0%
% of Gross Profit
Operating Expenses
YoY Change
Operating Profit
YoY Change
Interest Expense		$109.9M	$16.80M
YoY Change		15.81%	-61.29%
% of Operating Profit
Other Income/Expense, Net
YoY Change
Pretax Income	$310.0M	$1.123B	$240.6M
YoY Change	28.84%	80.4%	55.93%
Income Tax	$64.00M	$223.8M	$47.00M
% Of Pretax Income	20.65%	19.93%	19.53%
Net Earnings	$246.0M	$899.2M	$193.6M
YoY Change	27.07%	77.5%	51.13%
Net Earnings / Revenue		54.21%	58.38%
Basic Earnings Per Share		$8.72	$1.94
Diluted Earnings Per Share	$2.354M	$8.67	$1.93
COMMON SHARES
Basic Shares Outstanding	104.2M shares	102.7M shares	100.8M shares
Diluted Shares Outstanding		103.3M shares

Balance Sheet

Concept	2021 Q4	2021	2020 Q4
SHORT-TERM ASSETS
Cash & Short-Term Investments
YoY Change
Cash & Equivalents	$516.4M		$2.672B
Short-Term Investments
Other Short-Term Assets
YoY Change
Inventory
Prepaid Expenses
Receivables
Other Receivables
Total Short-Term Assets
YoY Change
LONG-TERM ASSETS
Property, Plant & Equipment	$182.0M	$315.0M	$134.1M
YoY Change	35.72%	52.17%	6.6%
Goodwill	$491.3M		$289.9M
YoY Change	69.47%		0.0%
Intangibles
YoY Change
Long-Term Investments	$159.0M	$159.0M	$167.0M
YoY Change	-4.79%	-4.79%	20.14%
Other Assets	$21.00M	$21.00M	$31.00M
YoY Change	-32.26%	-32.26%	72.22%
Total Long-Term Assets
YoY Change
TOTAL ASSETS
Total Short-Term Assets
Total Long-Term Assets
Total Assets	$55.98B	$55.98B	$36.46B
YoY Change	53.54%	53.54%	35.94%
SHORT-TERM LIABILITIES
YoY Change
Accounts Payable
YoY Change
Accrued Expenses	$143.0M	$143.0M	$80.00M
YoY Change	78.75%	78.75%	2.56%
Deferred Revenue
YoY Change
Short-Term Debt	$727.0M	$727.0M	$21.00M
YoY Change	3361.9%	4443.75%
Long-Term Debt Due
YoY Change
Total Short-Term Liabilities	$143.0M	$143.0M	$80.00M
YoY Change	78.75%	78.75%	2.56%
LONG-TERM LIABILITIES
Long-Term Debt	$1.671B	$1.671B	$549.0M
YoY Change	204.37%	204.37%	39.34%
Other Long-Term Liabilities	$868.0M	$868.0M	$467.0M
YoY Change	85.87%	85.87%	-10.19%
Total Long-Term Liabilities	$2.539B	$2.539B	$1.016B
YoY Change	149.9%	149.9%	11.16%
TOTAL LIABILITIES
Total Short-Term Liabilities	$143.0M	$143.0M	$80.00M
Total Long-Term Liabilities	$2.539B	$2.539B	$1.016B
Total Liabilities	$51.02B	$51.02B	$33.05B
YoY Change	54.38%	54.38%	38.82%
SHAREHOLDERS EQUITY
Retained Earnings	$2.773B		$2.001B
YoY Change	38.55%		19.11%
Common Stock	$1.966B		$1.391B
YoY Change	41.35%		13908900.0%
Preferred Stock
YoY Change
Treasury Stock (at cost)	$87.00M		$71.10M
YoY Change	22.36%		13.4%
Treasury Stock Shares	2.350M shares		2.169M shares
Shareholders Equity	$4.963B	$4.963B	$3.414B
YoY Change
Total Liabilities & Shareholders Equity	$55.98B	$55.98B	$36.46B
YoY Change	53.54%	53.54%	35.94%

Cashflow Statement

Concept	2021 Q4	2021	2020 Q4
OPERATING ACTIVITIES
Net Income	$246.0M	$899.2M	$193.6M
YoY Change	27.07%	77.5%	51.13%
Depreciation, Depletion And Amortization	$8.100M	$20.70M	$5.800M
YoY Change	39.66%	36.18%	16.0%
Cash From Operating Activities	$615.0M	-$2.654B	$220.1M
YoY Change	179.42%	-496.0%	20.08%
INVESTING ACTIVITIES
Capital Expenditures	-$37.60M	-$69.40M	$6.300M
YoY Change	-696.83%	158.96%	-131.82%
Acquisitions		$1.024B
YoY Change
Other Investing Activities	-$4.006B	-$14.64B	-$1.952B
YoY Change	105.25%	94.96%	110.33%
Cash From Investing Activities	-$4.044B	-$14.71B	-$1.946B
YoY Change	107.85%	95.18%	105.28%
FINANCING ACTIVITIES
Cash Dividend Paid		$127.6M
YoY Change		25.96%
Common Stock Issuance & Retirement, Net		-$540.3M
YoY Change		-854.61%
Debt Paid & Issued, Net		$475.9M
YoY Change		534.53%
Cash From Financing Activities	3.027B	$15.21B	2.978B
YoY Change	1.65%	67.07%	810.55%
NET CHANGE
Cash From Operating Activities	615.0M	-$2.654B	220.1M
Cash From Investing Activities	-4.044B	-$14.71B	-1.946B
Cash From Financing Activities	3.027B	$15.21B	2.978B
Net Change In Cash	-401.5M	-$2.155B	1.253B
YoY Change	-132.05%	-196.34%	-386.44%
FREE CASH FLOW
Cash From Operating Activities	$615.0M	-$2.654B	$220.1M
Capital Expenditures	-$37.60M	-$69.40M	$6.300M
Free Cash Flow	$652.6M	-$2.585B	$213.8M
YoY Change	205.24%	-470.82%	5.27%

Facts In Submission

Frame	Concept Type	Concept / XBRL Key	Value	Unit
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CY2021	dei	Document Fiscal Period Focus DocumentFiscalPeriodFocus	FY
CY2021	dei	Amendment Flag AmendmentFlag	false
CY2021	dei	Document Type DocumentType	10-K
CY2021	dei	Document Annual Report DocumentAnnualReport	true
CY2021	dei	Document Period End Date DocumentPeriodEndDate	2021-12-31
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CY2021	dei	Entity File Number EntityFileNumber	001-32550
CY2021	dei	Entity Registrant Name EntityRegistrantName	WESTERN ALLIANCE BANCORPORATION
CY2021	dei	Entity Incorporation State Country Code EntityIncorporationStateCountryCode	DE
CY2021	dei	Entity Tax Identification Number EntityTaxIdentificationNumber	88-0365922
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CY2020	wal	Legal Professional And Director Fees LegalProfessionalAndDirectorFees	42200000	USD
CY2019	wal	Legal Professional And Director Fees LegalProfessionalAndDirectorFees	37000000.0	USD
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CY2020	us-gaap	Information Technology And Data Processing InformationTechnologyAndDataProcessing	35700000	USD
CY2019	us-gaap	Information Technology And Data Processing InformationTechnologyAndDataProcessing	30600000	USD
CY2021	us-gaap	Expense Related To Distribution Or Servicing And Underwriting Fees ExpenseRelatedToDistributionOrServicingAndUnderwritingFees	53500000	USD
CY2020	us-gaap	Expense Related To Distribution Or Servicing And Underwriting Fees ExpenseRelatedToDistributionOrServicingAndUnderwritingFees	0	USD
CY2019	us-gaap	Expense Related To Distribution Or Servicing And Underwriting Fees ExpenseRelatedToDistributionOrServicingAndUnderwritingFees	0	USD
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CY2019	us-gaap	Occupancy Net OccupancyNet	32600000	USD
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CY2020	wal	Non Interest Expense Deposit Costs NonInterestExpenseDepositCosts	18500000	USD
CY2019	wal	Non Interest Expense Deposit Costs NonInterestExpenseDepositCosts	31700000	USD
CY2021	us-gaap	Loan Processing Fee LoanProcessingFee	28800000	USD
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CY2019	us-gaap	Loan Processing Fee LoanProcessingFee	0	USD
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CY2020	us-gaap	General Insurance Expense GeneralInsuranceExpense	13300000	USD
CY2019	us-gaap	General Insurance Expense GeneralInsuranceExpense	11900000	USD
CY2021	us-gaap	Marketing Expense MarketingExpense	13500000	USD
CY2020	us-gaap	Marketing Expense MarketingExpense	9600000	USD
CY2019	us-gaap	Marketing Expense MarketingExpense	11200000	USD
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CY2020	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	0	USD
CY2019	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	0	USD
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CY2019	wal	Acquisition And Restructure Expenses AcquisitionAndRestructureExpenses	0	USD
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CY2020	wal	Net Loss Gain On Sales Valuations Of Repossessed Assets And Bank Premises Net NetLossGainOnSalesValuationsOfRepossessedAssetsAndBankPremisesNet	-1500000	USD
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CY2021	wal	Acquisition And Restructure Expenses AcquisitionAndRestructureExpenses	15300000	USD
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CY2020	us-gaap	Other Noninterest Expense OtherNoninterestExpense	36100000	USD
CY2019	us-gaap	Other Noninterest Expense OtherNoninterestExpense	43900000	USD
CY2021	us-gaap	Noninterest Expense NoninterestExpense	851400000	USD
CY2020	us-gaap	Noninterest Expense NoninterestExpense	491600000	USD
CY2019	us-gaap	Noninterest Expense NoninterestExpense	482000000.0	USD
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CY2020	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	622500000	USD
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CY2021	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	223800000	USD
CY2020	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	115900000	USD
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CY2020	us-gaap	Net Income Loss NetIncomeLoss	506600000	USD
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CY2021	us-gaap	Preferred Stock Dividends Income Statement Impact PreferredStockDividendsIncomeStatementImpact	3500000	USD
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CY2020	us-gaap	Net Income Loss NetIncomeLoss	506600000	USD
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CY2021	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax	0	USD
CY2020	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax	100000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax	100000	USD
CY2021	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	0	USD
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CY2020	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesTax	0	USD
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CY2020	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	67300000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	58600000	USD
CY2021	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	822600000	USD
CY2020	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	573900000	USD
CY2019	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	557800000	USD
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CY2019	us-gaap	Stock Issued During Period Value Restricted Stock Award Net Of Forfeitures StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures	26300000	USD
CY2019	us-gaap	Adjustments Related To Tax Withholding For Share Based Compensation AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation	9600000	USD
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CY2019	us-gaap	Dividends Common Stock Cash DividendsCommonStockCash	51300000	USD
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CY2020	us-gaap	Net Income Loss NetIncomeLoss	506600000	USD
CY2020	us-gaap	Stock Issued During Period Value Restricted Stock Award Net Of Forfeitures StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures	29100000	USD
CY2019Q4	us-gaap	Stockholders Equity StockholdersEquity	3016700000	USD
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CY2020	us-gaap	Adjustments Related To Tax Withholding For Share Based Compensation AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation	8400000	USD
CY2020	us-gaap	Stock Repurchased And Retired During Period Value StockRepurchasedAndRetiredDuringPeriodValue	71600000	USD
CY2020	us-gaap	Dividends Common Stock Cash DividendsCommonStockCash	101300000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	67300000	USD
CY2020Q4	us-gaap	Stockholders Equity StockholdersEquity	3413500000	USD
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CY2021	us-gaap	Stock Issued During Period Value Restricted Stock Award Net Of Forfeitures StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures	35000000.0	USD
CY2021	us-gaap	Adjustments Related To Tax Withholding For Share Based Compensation AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation	15700000	USD
CY2021	us-gaap	Stock Issued During Period Value New Issues StockIssuedDuringPeriodValueNewIssues	540300000	USD
CY2021	us-gaap	Dividends Preferred Stock Cash DividendsPreferredStockCash	3500000	USD
CY2021	us-gaap	Dividends Common Stock Cash DividendsCommonStockCash	124100000	USD
CY2021	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	-76600000	USD
CY2021Q4	us-gaap	Stockholders Equity StockholdersEquity	4962600000	USD
CY2021	us-gaap	Net Income Loss NetIncomeLoss	899200000	USD
CY2020	us-gaap	Net Income Loss NetIncomeLoss	506600000	USD
CY2019	us-gaap	Net Income Loss NetIncomeLoss	499200000	USD
CY2021	us-gaap	Provision For Loan Lease And Other Losses ProvisionForLoanLeaseAndOtherLosses	21400000	USD
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CY2019	us-gaap	Depreciation And Amortization DepreciationAndAmortization	18500000	USD
CY2021	us-gaap	Share Based Compensation ShareBasedCompensation	35100000	USD
CY2020	us-gaap	Share Based Compensation ShareBasedCompensation	28700000	USD
CY2019	us-gaap	Share Based Compensation ShareBasedCompensation	26200000	USD
CY2021	us-gaap	Deferred Income Taxes And Tax Credits DeferredIncomeTaxesAndTaxCredits	42000000.0	USD
CY2020	us-gaap	Deferred Income Taxes And Tax Credits DeferredIncomeTaxesAndTaxCredits	-25100000	USD
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CY2019	us-gaap	Accretion Amortization Of Discounts And Premiums Investments AccretionAmortizationOfDiscountsAndPremiumsInvestments	-17100000	USD
CY2021	us-gaap	Amortization Method Qualified Affordable Housing Project Investments Amortization AmortizationMethodQualifiedAffordableHousingProjectInvestmentsAmortization	49500000	USD
CY2020	us-gaap	Amortization Method Qualified Affordable Housing Project Investments Amortization AmortizationMethodQualifiedAffordableHousingProjectInvestmentsAmortization	49200000	USD
CY2019	us-gaap	Amortization Method Qualified Affordable Housing Project Investments Amortization AmortizationMethodQualifiedAffordableHousingProjectInvestmentsAmortization	41500000	USD
CY2021	us-gaap	Operating Lease Right Of Use Asset Amortization Expense OperatingLeaseRightOfUseAssetAmortizationExpense	16300000	USD
CY2020	us-gaap	Operating Lease Right Of Use Asset Amortization Expense OperatingLeaseRightOfUseAssetAmortizationExpense	11700000	USD
CY2019	us-gaap	Operating Lease Right Of Use Asset Amortization Expense OperatingLeaseRightOfUseAssetAmortizationExpense	10500000	USD
CY2021	us-gaap	Amortization Of Deferred Loan Origination Fees Net AmortizationOfDeferredLoanOriginationFeesNet	66300000	USD
CY2020	us-gaap	Amortization Of Deferred Loan Origination Fees Net AmortizationOfDeferredLoanOriginationFeesNet	51200000	USD
CY2019	us-gaap	Amortization Of Deferred Loan Origination Fees Net AmortizationOfDeferredLoanOriginationFeesNet	42700000	USD
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CY2020	us-gaap	Payments For Origination And Purchases Of Loans Held For Sale PaymentsForOriginationAndPurchasesOfLoansHeldForSale	0	USD
CY2019	us-gaap	Payments For Origination And Purchases Of Loans Held For Sale PaymentsForOriginationAndPurchasesOfLoansHeldForSale	0	USD
CY2021	us-gaap	Proceeds From Sale And Collection Of Loans Heldforsale ProceedsFromSaleAndCollectionOfLoansHeldforsale	56647700000	USD
CY2020	us-gaap	Proceeds From Sale And Collection Of Loans Heldforsale ProceedsFromSaleAndCollectionOfLoansHeldforsale	0	USD
CY2019	us-gaap	Proceeds From Sale And Collection Of Loans Heldforsale ProceedsFromSaleAndCollectionOfLoansHeldforsale	0	USD
CY2021	us-gaap	Servicing Asset At Fair Value Additions ServicingAssetAtFairValueAdditions	763800000	USD
CY2020	us-gaap	Servicing Asset At Fair Value Additions ServicingAssetAtFairValueAdditions	0	USD
CY2019	us-gaap	Servicing Asset At Fair Value Additions ServicingAssetAtFairValueAdditions	0	USD
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CY2020	us-gaap	Servicing Asset At Fair Value Period Increase Decrease ServicingAssetAtFairValuePeriodIncreaseDecrease	0	USD
CY2019	us-gaap	Servicing Asset At Fair Value Period Increase Decrease ServicingAssetAtFairValuePeriodIncreaseDecrease	0	USD
CY2021	us-gaap	Other Operating Activities Cash Flow Statement OtherOperatingActivitiesCashFlowStatement	16300000	USD
CY2020	us-gaap	Other Operating Activities Cash Flow Statement OtherOperatingActivitiesCashFlowStatement	9400000	USD
CY2019	us-gaap	Other Operating Activities Cash Flow Statement OtherOperatingActivitiesCashFlowStatement	5100000	USD
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CY2021	us-gaap	Payments To Acquire Available For Sale Securities Debt PaymentsToAcquireAvailableForSaleSecuritiesDebt	3248400000	USD
CY2020	us-gaap	Payments To Acquire Available For Sale Securities Debt PaymentsToAcquireAvailableForSaleSecuritiesDebt	2966200000	USD
CY2019	us-gaap	Payments To Acquire Available For Sale Securities Debt PaymentsToAcquireAvailableForSaleSecuritiesDebt	927600000	USD
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CY2020	wal	Paymentsto Acquire Securities Equity PaymentstoAcquireSecuritiesEquity	34500000	USD
CY2019	wal	Paymentsto Acquire Securities Equity PaymentstoAcquireSecuritiesEquity	32700000	USD
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CY2021	us-gaap	Proceeds From Sale Of Equity Securities Fv Ni ProceedsFromSaleOfEquitySecuritiesFvNi	4400000	USD
CY2020	us-gaap	Proceeds From Sale Of Equity Securities Fv Ni ProceedsFromSaleOfEquitySecuritiesFvNi	0	USD
CY2019	us-gaap	Proceeds From Sale Of Equity Securities Fv Ni ProceedsFromSaleOfEquitySecuritiesFvNi	0	USD
CY2021	us-gaap	Proceeds From Sale Of Mortgage Servicing Rights Msr ProceedsFromSaleOfMortgageServicingRightsMSR	1182800000	USD
CY2020	us-gaap	Proceeds From Sale Of Mortgage Servicing Rights Msr ProceedsFromSaleOfMortgageServicingRightsMSR	0	USD
CY2019	us-gaap	Proceeds From Sale Of Mortgage Servicing Rights Msr ProceedsFromSaleOfMortgageServicingRightsMSR	0	USD
CY2021	wal	Purchase Of Other Investments PurchaseOfOtherInvestments	134600000	USD
CY2020	wal	Purchase Of Other Investments PurchaseOfOtherInvestments	133100000	USD
CY2019	wal	Purchase Of Other Investments PurchaseOfOtherInvestments	150800000	USD
CY2021	us-gaap	Proceeds From Life Insurance Policies ProceedsFromLifeInsurancePolicies	0	USD
CY2020	us-gaap	Proceeds From Life Insurance Policies ProceedsFromLifeInsurancePolicies	5900000	USD
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CY2021	us-gaap	Payments For Proceeds From Loans And Leases PaymentsForProceedsFromLoansAndLeases	12665000000	USD
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CY2019	us-gaap	Payments For Proceeds From Loans And Leases PaymentsForProceedsFromLoansAndLeases	3429000000	USD
CY2021	us-gaap	Payments For Proceeds From Productive Assets PaymentsForProceedsFromProductiveAssets	69400000	USD
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CY2019	us-gaap	Payments For Proceeds From Productive Assets PaymentsForProceedsFromProductiveAssets	33800000	USD
CY2021	us-gaap	Payments To Acquire Businesses Net Of Cash Acquired PaymentsToAcquireBusinessesNetOfCashAcquired	1024400000	USD
CY2020	us-gaap	Payments To Acquire Businesses Net Of Cash Acquired PaymentsToAcquireBusinessesNetOfCashAcquired	0	USD
CY2019	us-gaap	Payments To Acquire Businesses Net Of Cash Acquired PaymentsToAcquireBusinessesNetOfCashAcquired	0	USD
CY2021	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-14711900000	USD
CY2020	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-7537500000	USD
CY2019	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-3723000000	USD
CY2021	us-gaap	Increase Decrease In Deposits IncreaseDecreaseInDeposits	15681500000	USD
CY2020	us-gaap	Increase Decrease In Deposits IncreaseDecreaseInDeposits	9134000000	USD
CY2019	us-gaap	Increase Decrease In Deposits IncreaseDecreaseInDeposits	3619000000	USD
CY2021	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	1055700000	USD
CY2020	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	221900000	USD
CY2019	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	0	USD
CY2021	us-gaap	Repayments Of Long Term Debt RepaymentsOfLongTermDebt	475900000	USD
CY2020	us-gaap	Repayments Of Long Term Debt RepaymentsOfLongTermDebt	75000000.0	USD
CY2019	us-gaap	Repayments Of Long Term Debt RepaymentsOfLongTermDebt	0	USD
CY2021	us-gaap	Proceeds From Repayments Of Debt ProceedsFromRepaymentsOfDebt	-1742100000	USD
CY2020	us-gaap	Proceeds From Repayments Of Debt ProceedsFromRepaymentsOfDebt	4300000	USD
CY2019	us-gaap	Proceeds From Repayments Of Debt ProceedsFromRepaymentsOfDebt	-496700000	USD
CY2021	us-gaap	Payments Related To Tax Withholding For Share Based Compensation PaymentsRelatedToTaxWithholdingForShareBasedCompensation	15800000	USD
CY2020	us-gaap	Payments Related To Tax Withholding For Share Based Compensation PaymentsRelatedToTaxWithholdingForShareBasedCompensation	7900000	USD
CY2019	us-gaap	Payments Related To Tax Withholding For Share Based Compensation PaymentsRelatedToTaxWithholdingForShareBasedCompensation	9600000	USD
CY2021	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	0	USD
CY2020	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	71600000	USD
CY2019	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	120200000	USD
CY2021	us-gaap	Payments Of Dividends PaymentsOfDividends	127600000	USD
CY2020	us-gaap	Payments Of Dividends PaymentsOfDividends	101300000	USD
CY2019	us-gaap	Payments Of Dividends PaymentsOfDividends	51300000	USD
CY2021	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	540300000	USD
CY2020	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	0	USD
CY2019	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	0	USD
CY2021	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	15210600000	USD
CY2020	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	9104400000	USD
CY2019	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	2941200000	USD
CY2021	us-gaap	Cash And Cash Equivalents Period Increase Decrease CashAndCashEquivalentsPeriodIncreaseDecrease	-2155300000	USD
CY2020	us-gaap	Cash And Cash Equivalents Period Increase Decrease CashAndCashEquivalentsPeriodIncreaseDecrease	2237100000	USD
CY2019	us-gaap	Cash And Cash Equivalents Period Increase Decrease CashAndCashEquivalentsPeriodIncreaseDecrease	-64000000.0	USD
CY2020Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	2671700000	USD
CY2019Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	434600000	USD
CY2018Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	498600000	USD
CY2021Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	516400000	USD
CY2020Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	2671700000	USD
CY2019Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	434600000	USD
CY2021	us-gaap	Interest Paid InterestPaid	111600000	USD
CY2020	us-gaap	Interest Paid InterestPaid	108600000	USD
CY2019	us-gaap	Interest Paid InterestPaid	180400000	USD
CY2021	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	175700000	USD
CY2020	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	44200000	USD
CY2019	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	-23400000	USD
CY2021	wal	Net Increase Decrease In Unfunded Commitments And Obligations NetIncreaseDecreaseInUnfundedCommitmentsAndObligations	294100000	USD
CY2020	wal	Net Increase Decrease In Unfunded Commitments And Obligations NetIncreaseDecreaseInUnfundedCommitmentsAndObligations	-102200000	USD
CY2019	wal	Net Increase Decrease In Unfunded Commitments And Obligations NetIncreaseDecreaseInUnfundedCommitmentsAndObligations	36600000	USD
CY2021	wal	Transfers Of Securitized Lhfs To Afs Securities TransfersOfSecuritizedLHFSToAFSSecurities	144500000	USD
CY2020	wal	Transfers Of Securitized Lhfs To Afs Securities TransfersOfSecuritizedLHFSToAFSSecurities	0	USD
CY2019	wal	Transfers Of Securitized Lhfs To Afs Securities TransfersOfSecuritizedLHFSToAFSSecurities	0	USD
CY2021	us-gaap	Use Of Estimates UseOfEstimates	Use of estimatesThe preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Management's estimates and judgments are ongoing and are based on experience, current and expected future conditions, third-party evaluations and various other assumptions that management believes are reasonable under the circumstances. The results of these estimates form the basis for making judgments about the carrying values of assets and liabilities, as well as identifying and assessing the accounting treatment with respect to commitments and contingencies. Actual results may differ from those estimates and assumptions used in the Consolidated Financial Statements and related notes. Material estimates that are susceptible to significant changes in the near term, particularly to the extent that economic conditions worsen or persist longer than expected in an adverse state, relate to: 1) the determination of the allowance for credit losses; 2) certain assets and liabilities carried at fair value; and 3) accounting for income taxes.
CY2021	wal	Number Of Unconsolidated Subsidiaries NumberOfUnconsolidatedSubsidiaries	8	Subsidiary
CY2021	us-gaap	Prior Period Reclassification Adjustment Description PriorPeriodReclassificationAdjustmentDescription	ReclassificationsCertain amounts in the Consolidated Income Statements for the prior periods have been reclassified to conform to the current presentation. The reclassifications have no effect on net income or stockholders’ equity as previously reported.
CY2021	us-gaap	Payments To Acquire Businesses Gross PaymentsToAcquireBusinessesGross	1200000000	USD
CY2021Q4	us-gaap	Life Insurance Corporate Or Bank Owned Amount LifeInsuranceCorporateOrBankOwnedAmount	462500000	USD
CY2020Q4	us-gaap	Life Insurance Corporate Or Bank Owned Amount LifeInsuranceCorporateOrBankOwnedAmount	465800000	USD
CY2021	wal	Acquisition And Restructure Expenses AcquisitionAndRestructureExpenses	15300000	USD
CY2021	us-gaap	Business Combination Acquisition Related Costs BusinessCombinationAcquisitionRelatedCosts	3400000	USD
CY2021	wal	Business Combination Provisional Information Initial Accounting Incomplete Adjustment Servicing Right Asset BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentServicingRightAsset	29.3	USD
CY2021Q2	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Cash And Equivalents BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents	207200000	USD
CY2021Q2	wal	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Loans Held For Sale BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLoansHeldForSale	3552900000	USD
CY2021Q2	wal	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Servicing Assets BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedServicingAssets	1347000000	USD
CY2021Q2	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Property Plant And Equipment BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment	11300000	USD
CY2021Q2	wal	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Operating Right Of Use Asset BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingRightOfUseAsset	18900000	USD
CY2021Q2	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Intangibles BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles	141000000.0	USD
CY2021Q2	wal	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Loans Eligible For Repurchase BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLoansEligibleForRepurchase	2744700000	USD
CY2021Q2	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deferred Tax Assets BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssets	6600000	USD
CY2021Q2	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Other Noncurrent Assets BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets	236000000.0	USD
CY2021Q2	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Assets BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets	8265600000	USD
CY2021Q2	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Liabilities Long Term Debt BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLongTermDebt	3633900000	USD
CY2021Q2	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Capital Lease Obligation BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCapitalLeaseObligation	18900000	USD
CY2021Q2	wal	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Liability For Loans Eligible For Repurchase BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilityForLoansEligibleForRepurchase	2744700000	USD
CY2021Q2	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Liabilities Other BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther	151100000	USD
CY2021Q2	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Liabilities BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities	6548600000	USD
CY2021Q2	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Net BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet	1717000000	USD
CY2021	us-gaap	Payments To Acquire Businesses Gross PaymentsToAcquireBusinessesGross	1231600000	USD
CY2021Q4	wal	Business Combination Elimination Of Pre Existing Debt And Other BusinessCombinationEliminationOfPreExistingDebtAndOther	686800000	USD
CY2021	us-gaap	Business Combination Consideration Transferred1 BusinessCombinationConsiderationTransferred1	1918400000	USD
CY2021Q2	us-gaap	Goodwill Goodwill	201400000	USD
CY2021Q2	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Intangibles BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles	141000000	USD
CY2021Q2	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Intangibles BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles	141000000.0	USD
CY2021Q2	us-gaap	Goodwill Goodwill	201400000	USD
CY2021Q2	us-gaap	Business Acquisition Purchase Price Allocation Goodwill Expected Tax Deductible Amount BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount	185000000	USD
CY2021	wal	Business Acquisition Pro Forma Interest Income BusinessAcquisitionProFormaInterestIncome	1679900000	USD
CY2020	wal	Business Acquisition Pro Forma Interest Income BusinessAcquisitionProFormaInterestIncome	1322600000	USD
CY2021	wal	Business Acquisition Pro Forma Non Interest Income BusinessAcquisitionProFormaNonInterestIncome	470500000	USD
CY2020	wal	Business Acquisition Pro Forma Non Interest Income BusinessAcquisitionProFormaNonInterestIncome	902700000	USD
CY2021	us-gaap	Business Acquisitions Pro Forma Net Income Loss BusinessAcquisitionsProFormaNetIncomeLoss	909700000	USD
CY2020	us-gaap	Business Acquisitions Pro Forma Net Income Loss BusinessAcquisitionsProFormaNetIncomeLoss	931200000	USD
CY2021Q4	us-gaap	Held To Maturity Securities HeldToMaturitySecurities	1107100000	USD
CY2021Q4	us-gaap	Held To Maturity Securities Accumulated Unrecognized Holding Gain HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain	43200000	USD
CY2021Q4	us-gaap	Held To Maturity Securities Accumulated Unrecognized Holding Loss HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss	3900000	USD
CY2021Q4	us-gaap	Held To Maturity Securities Fair Value HeldToMaturitySecuritiesFairValue	1146400000	USD
CY2021Q4	us-gaap	Available For Sale Debt Securities Amortized Cost Basis AvailableForSaleDebtSecuritiesAmortizedCostBasis	6166500000	USD
CY2021Q4	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Gain Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax	103600000	USD
CY2021Q4	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Loss Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax	81300000	USD
CY2021Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	6188800000	USD
CY2021Q4	us-gaap	Equity Securities Fv Ni Cost EquitySecuritiesFvNiCost	152200000	USD
CY2021Q4	wal	Equitysecurities Fvni Accumulated Gross Unrealized Gain Before Tax EquitysecuritiesFVNIAccumulatedGrossUnrealizedGainBeforeTax	7700000	USD
CY2021Q4	wal	Equitysecurities Fvni Accumulated Gross Unrealized Loss Before Tax EquitysecuritiesFVNIAccumulatedGrossUnrealizedLossBeforeTax	1400000	USD
CY2021Q4	us-gaap	Equity Securities Fv Ni EquitySecuritiesFvNi	158500000	USD
CY2020Q4	us-gaap	Held To Maturity Securities HeldToMaturitySecurities	568800000	USD
CY2020Q4	us-gaap	Held To Maturity Securities Accumulated Unrecognized Holding Gain HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain	43000000.0	USD
CY2020Q4	us-gaap	Held To Maturity Securities Accumulated Unrecognized Holding Loss HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss	0	USD
CY2020Q4	us-gaap	Held To Maturity Securities Fair Value HeldToMaturitySecuritiesFairValue	611800000	USD
CY2020Q4	us-gaap	Available For Sale Debt Securities Amortized Cost Basis AvailableForSaleDebtSecuritiesAmortizedCostBasis	4586400000	USD
CY2020Q4	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Gain Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax	137600000	USD
CY2020Q4	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Loss Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax	15500000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	4708500000	USD
CY2020Q4	us-gaap	Equity Securities Fv Ni Cost EquitySecuritiesFvNiCost	160100000	USD
CY2020Q4	wal	Equitysecurities Fvni Accumulated Gross Unrealized Gain Before Tax EquitysecuritiesFVNIAccumulatedGrossUnrealizedGainBeforeTax	7600000	USD
CY2020Q4	wal	Equitysecurities Fvni Accumulated Gross Unrealized Loss Before Tax EquitysecuritiesFVNIAccumulatedGrossUnrealizedLossBeforeTax	400000	USD
CY2020Q4	us-gaap	Equity Securities Fv Ni EquitySecuritiesFvNi	167300000	USD
CY2021Q4	us-gaap	Pledged Financial Instruments Not Separately Reported Other Debt Securities Available For Sale Or Held For Investment PledgedFinancialInstrumentsNotSeparatelyReportedOtherDebtSecuritiesAvailableForSaleOrHeldForInvestment	2200000000	USD
CY2020Q4	us-gaap	Pledged Financial Instruments Not Separately Reported Other Debt Securities Available For Sale Or Held For Investment PledgedFinancialInstrumentsNotSeparatelyReportedOtherDebtSecuritiesAvailableForSaleOrHeldForInvestment	778000000	USD
CY2021Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss	67900000	USD
CY2021Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months	3046300000	USD
CY2021Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss	13400000	USD
CY2021Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger	169500000	USD
CY2021Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position Accumulated Loss DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss	81300000	USD
CY2021Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position DebtSecuritiesAvailableForSaleUnrealizedLossPosition	3215800000	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss	4400000	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months	398900000	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss	11100000	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger	120800000	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position Accumulated Loss DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss	15500000	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position DebtSecuritiesAvailableForSaleUnrealizedLossPosition	519700000	USD
CY2021Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position Number Of Positions DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions	179	positions
CY2020Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position Number Of Positions DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions	49	positions
CY2020Q4	us-gaap	Debt Securities Held To Maturity Allowance For Credit Loss DebtSecuritiesHeldToMaturityAllowanceForCreditLoss	6800000	USD
CY2021	us-gaap	Debt Securities Held To Maturity Credit Loss Expense Reversal DebtSecuritiesHeldToMaturityCreditLossExpenseReversal	-1600000	USD
CY2021	us-gaap	Debt Securities Held To Maturity Allowance For Credit Loss Writeoff DebtSecuritiesHeldToMaturityAllowanceForCreditLossWriteoff	0	USD
CY2021	us-gaap	Debt Securities Held To Maturity Allowance For Credit Loss Recovery DebtSecuritiesHeldToMaturityAllowanceForCreditLossRecovery	0	USD
CY2021Q4	us-gaap	Debt Securities Held To Maturity Allowance For Credit Loss DebtSecuritiesHeldToMaturityAllowanceForCreditLoss	5200000	USD
CY2020Q1	us-gaap	Debt Securities Held To Maturity Allowance For Credit Loss DebtSecuritiesHeldToMaturityAllowanceForCreditLoss	2700000	USD
CY2020	us-gaap	Debt Securities Held To Maturity Credit Loss Expense Reversal DebtSecuritiesHeldToMaturityCreditLossExpenseReversal	4100000	USD
CY2020	us-gaap	Debt Securities Held To Maturity Allowance For Credit Loss Writeoff DebtSecuritiesHeldToMaturityAllowanceForCreditLossWriteoff	0	USD
CY2020	us-gaap	Debt Securities Held To Maturity Allowance For Credit Loss Recovery DebtSecuritiesHeldToMaturityAllowanceForCreditLossRecovery	0	USD
CY2020Q4	us-gaap	Debt Securities Held To Maturity Allowance For Credit Loss DebtSecuritiesHeldToMaturityAllowanceForCreditLoss	6800000	USD
CY2021Q4	us-gaap	Accrued Investment Income Receivable AccruedInvestmentIncomeReceivable	3000000	USD
CY2020Q4	us-gaap	Accrued Investment Income Receivable AccruedInvestmentIncomeReceivable	2000000	USD
CY2021Q4	us-gaap	Held To Maturity Securities HeldToMaturitySecurities	1107100000	USD
CY2021Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	6188800000	USD
CY2021Q4	us-gaap	Equity Securities Fv Ni EquitySecuritiesFvNi	158500000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	4708500000	USD
CY2020Q4	us-gaap	Equity Securities Fv Ni EquitySecuritiesFvNi	167300000	USD
CY2021Q4	us-gaap	Held To Maturity Securities Debt Maturities Within One Year Net Carrying Amount HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearNetCarryingAmount	40700000	USD
CY2021Q4	us-gaap	Held To Maturity Securities Debt Maturities Within One Year Fair Value HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearFairValue	40700000	USD
CY2021Q4	us-gaap	Held To Maturity Securities Debt Maturities After One Through Five Years Net Carrying Amount HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsNetCarryingAmount	18100000	USD
CY2021Q4	us-gaap	Held To Maturity Securities Debt Maturities After One Through Five Years Fair Value HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue	18000000.0	USD
CY2021Q4	us-gaap	Held To Maturity Securities Debt Maturities After Ten Years Net Carrying Amount HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsNetCarryingAmount	831400000	USD
CY2021Q4	us-gaap	Held To Maturity Securities Debt Maturities After Ten Years Fair Value HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsFairValue	872400000	USD
CY2021Q4	us-gaap	Held To Maturity Securities Debt Maturities Without Single Maturity Date Net Carrying Amount HeldToMaturitySecuritiesDebtMaturitiesWithoutSingleMaturityDateNetCarryingAmount	216900000	USD
CY2021Q4	us-gaap	Held To Maturity Securities Debt Maturities Without Single Maturity Date Fair Value HeldToMaturitySecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue	215300000	USD
CY2021Q4	us-gaap	Held To Maturity Securities HeldToMaturitySecurities	1107100000	USD
CY2021Q4	us-gaap	Held To Maturity Securities Fair Value HeldToMaturitySecuritiesFairValue	1146400000	USD
CY2021Q4	us-gaap	Available For Sale Securities Debt Maturities Within One Year Amortized Cost AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost	14000000.0	USD
CY2021Q4	us-gaap	Available For Sale Securities Debt Maturities Within One Year Fair Value AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue	14000000.0	USD
CY2021Q4	us-gaap	Available For Sale Securities Debt Maturities After One Through Five Years Amortized Cost AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost	119200000	USD
CY2021Q4	us-gaap	Available For Sale Securities Debt Maturities After One Through Five Years Fair Value AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue	115800000	USD
CY2021Q4	us-gaap	Available For Sale Securities Debt Maturities After Five Through Ten Years Amortized Cost AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost	760400000	USD
CY2021Q4	us-gaap	Available For Sale Securities Debt Maturities After Five Through Ten Years Fair Value AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue	765200000	USD
CY2021Q4	us-gaap	Available For Sale Securities Debt Maturities After Ten Years Amortized Cost AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost	1648500000	USD
CY2021Q4	us-gaap	Available For Sale Securities Debt Maturities After Ten Years Fair Value AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue	1723900000	USD
CY2021Q4	us-gaap	Available For Sale Securities Debt Maturities Without Single Maturity Date Amortized Cost AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost	3624400000	USD
CY2021Q4	us-gaap	Available For Sale Securities Debt Maturities Without Single Maturity Date Fair Value AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue	3569900000	USD
CY2021Q4	us-gaap	Available For Sale Debt Securities Amortized Cost Basis AvailableForSaleDebtSecuritiesAmortizedCostBasis	6166500000	USD
CY2021Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	6188800000	USD
CY2021	us-gaap	Debt Securities Available For Sale Realized Gain DebtSecuritiesAvailableForSaleRealizedGain	8400000	USD
CY2020	us-gaap	Debt Securities Available For Sale Realized Gain DebtSecuritiesAvailableForSaleRealizedGain	400000	USD
CY2019	us-gaap	Debt Securities Available For Sale Realized Gain DebtSecuritiesAvailableForSaleRealizedGain	3100000	USD
CY2021	us-gaap	Debt Securities Available For Sale Realized Loss DebtSecuritiesAvailableForSaleRealizedLoss	0	USD
CY2020	us-gaap	Debt Securities Available For Sale Realized Loss DebtSecuritiesAvailableForSaleRealizedLoss	200000	USD
CY2019	us-gaap	Debt Securities Available For Sale Realized Loss DebtSecuritiesAvailableForSaleRealizedLoss	0	USD
CY2021	us-gaap	Debt Securities Available For Sale Realized Gain Loss DebtSecuritiesAvailableForSaleRealizedGainLoss	8400000	USD
CY2020	us-gaap	Debt Securities Available For Sale Realized Gain Loss DebtSecuritiesAvailableForSaleRealizedGainLoss	200000	USD
CY2019	us-gaap	Debt Securities Available For Sale Realized Gain Loss DebtSecuritiesAvailableForSaleRealizedGainLoss	3100000	USD
CY2021	us-gaap	Equity Securities Fv Ni Realized Gain EquitySecuritiesFvNiRealizedGain	100000	USD
CY2020	us-gaap	Equity Securities Fv Ni Realized Gain EquitySecuritiesFvNiRealizedGain	0	USD
CY2019	us-gaap	Equity Securities Fv Ni Realized Gain EquitySecuritiesFvNiRealizedGain	0	USD
CY2021	us-gaap	Equity Securities Fv Ni Realized Loss EquitySecuritiesFvNiRealizedLoss	200000	USD
CY2020	us-gaap	Equity Securities Fv Ni Realized Loss EquitySecuritiesFvNiRealizedLoss	0	USD
CY2019	us-gaap	Equity Securities Fv Ni Realized Loss EquitySecuritiesFvNiRealizedLoss	0	USD
CY2021	us-gaap	Equity Securities Fv Ni Realized Gain Loss EquitySecuritiesFvNiRealizedGainLoss	-100000	USD
CY2020	us-gaap	Equity Securities Fv Ni Realized Gain Loss EquitySecuritiesFvNiRealizedGainLoss	0	USD
CY2019	us-gaap	Equity Securities Fv Ni Realized Gain Loss EquitySecuritiesFvNiRealizedGainLoss	0	USD
CY2021	us-gaap	Debt Securities Available For Sale Realized Gain Loss DebtSecuritiesAvailableForSaleRealizedGainLoss	8400000	USD
CY2019	us-gaap	Debt Securities Available For Sale Realized Gain Loss DebtSecuritiesAvailableForSaleRealizedGainLoss	3100000	USD
CY2021Q4	us-gaap	Loans Receivable Held For Sale Amount LoansReceivableHeldForSaleAmount	5635100000	USD
CY2021Q4	us-gaap	Pledged Assets Separately Reported Loans Pledged As Collateral At Fair Value PledgedAssetsSeparatelyReportedLoansPledgedAsCollateralAtFairValue	0	USD
CY2021	wal	Msr Capitalized Upon Sale Of Loan MSRCapitalizedUponSaleOfLoan	763800000	USD
CY2021	us-gaap	Proceeds From Sale Of Mortgage Loans Held For Sale ProceedsFromSaleOfMortgageLoansHeldForSale	465300000	USD
CY2021	wal	Provision For And Change In Estimate Of Liability For Losses Under Representations And Warranties ProvisionForAndChangeInEstimateOfLiabilityForLossesUnderRepresentationsAndWarranties	600000	USD
CY2021	wal	Change In Fair Value Of Loans Held For Sale ChangeInFairValueOfLoansHeldForSale	-300000	USD
CY2021	us-gaap	Unrealized Gain Loss On Derivatives UnrealizedGainLossOnDerivatives	69900000	USD
CY2021	us-gaap	Derivative Instruments Not Designated As Hedging Instruments Gain DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGain	20100000	USD
CY2021	us-gaap	Gain Loss On Sales Of Loans Net GainLossOnSalesOfLoansNet	247800000	USD
CY2021	wal	Loan Acquisition And Origination Fees LoanAcquisitionAndOriginationFees	78400000	USD
CY2021	wal	Net Gain On Loan Origination And Sale Activities NetGainOnLoanOriginationAndSaleActivities	326200000	USD
CY2021Q4	us-gaap	Loans And Leases Receivable Net Of Deferred Income LoansAndLeasesReceivableNetOfDeferredIncome	39075400000	USD
CY2020Q4	us-gaap	Loans And Leases Receivable Net Of Deferred Income LoansAndLeasesReceivableNetOfDeferredIncome	27053000000	USD
CY2021Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	252500000	USD
CY2020Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	278900000	USD
CY2021Q4	us-gaap	Loans And Leases Receivable Net Reported Amount LoansAndLeasesReceivableNetReportedAmount	38822900000	USD
CY2020Q4	us-gaap	Loans And Leases Receivable Net Reported Amount LoansAndLeasesReceivableNetReportedAmount	26774100000	USD
CY2021Q4	us-gaap	Loans And Leases Receivable Deferred Income LoansAndLeasesReceivableDeferredIncome	85700000	USD
CY2020Q4	us-gaap	Loans And Leases Receivable Deferred Income LoansAndLeasesReceivableDeferredIncome	75400000	USD
CY2021Q4	us-gaap	Receivable With Imputed Interest Premium ReceivableWithImputedInterestPremium	184800000	USD
CY2020Q4	us-gaap	Receivable With Imputed Interest Premium ReceivableWithImputedInterestPremium	26000000	USD
CY2021Q4	us-gaap	Financing Receivable Nonaccrual No Allowance FinancingReceivableNonaccrualNoAllowance	38900000	USD
CY2021Q4	wal	Financing Receivable Nonaccrual With Allowance FinancingReceivableNonaccrualWithAllowance	33700000	USD
CY2021Q4	us-gaap	Financing Receivable Recorded Investment Nonaccrual Status FinancingReceivableRecordedInvestmentNonaccrualStatus	72600000	USD
CY2021Q4	us-gaap	Financing Receivable Recorded Investment90 Days Past Due And Still Accruing FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing	0	USD
CY2020Q4	us-gaap	Financing Receivable Nonaccrual No Allowance FinancingReceivableNonaccrualNoAllowance	104900000	USD
CY2020Q4	wal	Financing Receivable Nonaccrual With Allowance FinancingReceivableNonaccrualWithAllowance	10300000	USD
CY2020Q4	us-gaap	Financing Receivable Recorded Investment Nonaccrual Status FinancingReceivableRecordedInvestmentNonaccrualStatus	115200000	USD
CY2020Q4	us-gaap	Financing Receivable Recorded Investment90 Days Past Due And Still Accruing FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing	0	USD
CY2021	us-gaap	Loans And Leases Receivable Impaired Interest Lost On Nonaccrual Loans LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans	5300000	USD
CY2020	us-gaap	Loans And Leases Receivable Impaired Interest Lost On Nonaccrual Loans LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans	5000000	USD
CY2019	us-gaap	Loans And Leases Receivable Impaired Interest Lost On Nonaccrual Loans LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans	2200000	USD
CY2021Q4	us-gaap	Loans And Leases Receivable Net Of Deferred Income LoansAndLeasesReceivableNetOfDeferredIncome	39075400000	USD
CY2020Q4	us-gaap	Loans And Leases Receivable Net Of Deferred Income LoansAndLeasesReceivableNetOfDeferredIncome	27053000000	USD
CY2021Q4	us-gaap	Financing Receivable Originated In Current Fiscal Year FinancingReceivableOriginatedInCurrentFiscalYear	15115400000	USD
CY2021Q4	us-gaap	Financing Receivable Originated In Fiscal Year Before Latest Fiscal Year FinancingReceivableOriginatedInFiscalYearBeforeLatestFiscalYear	3624200000	USD
CY2021Q4	us-gaap	Financing Receivable Originated Two Years Before Latest Fiscal Year FinancingReceivableOriginatedTwoYearsBeforeLatestFiscalYear	3176000000	USD
CY2021Q4	us-gaap	Financing Receivable Originated Three Years Before Latest Fiscal Year FinancingReceivableOriginatedThreeYearsBeforeLatestFiscalYear	1495400000	USD
CY2020Q4	us-gaap	Financing Receivable Revolving FinancingReceivableRevolving	8919500000	USD
CY2021Q4	us-gaap	Financing Receivable Originated Four Years Before Latest Fiscal Year FinancingReceivableOriginatedFourYearsBeforeLatestFiscalYear	976300000	USD
CY2021Q4	us-gaap	Financing Receivable Originated Five Or More Years Before Latest Fiscal Year FinancingReceivableOriginatedFiveOrMoreYearsBeforeLatestFiscalYear	1835600000	USD
CY2021Q4	us-gaap	Financing Receivable Revolving FinancingReceivableRevolving	12852500000	USD
CY2021Q4	us-gaap	Loans And Leases Receivable Net Of Deferred Income LoansAndLeasesReceivableNetOfDeferredIncome	39075400000	USD
CY2020Q4	us-gaap	Financing Receivable Originated In Current Fiscal Year FinancingReceivableOriginatedInCurrentFiscalYear	6006000000	USD
CY2020Q4	us-gaap	Financing Receivable Originated In Fiscal Year Before Latest Fiscal Year FinancingReceivableOriginatedInFiscalYearBeforeLatestFiscalYear	4935500000	USD
CY2020Q4	us-gaap	Financing Receivable Originated Two Years Before Latest Fiscal Year FinancingReceivableOriginatedTwoYearsBeforeLatestFiscalYear	2939200000	USD
CY2020Q4	us-gaap	Financing Receivable Originated Three Years Before Latest Fiscal Year FinancingReceivableOriginatedThreeYearsBeforeLatestFiscalYear	1669000000	USD
CY2020Q4	us-gaap	Financing Receivable Originated Four Years Before Latest Fiscal Year FinancingReceivableOriginatedFourYearsBeforeLatestFiscalYear	691400000	USD
CY2020Q4	us-gaap	Financing Receivable Originated Five Or More Years Before Latest Fiscal Year FinancingReceivableOriginatedFiveOrMoreYearsBeforeLatestFiscalYear	1892400000	USD
CY2020Q4	us-gaap	Loans And Leases Receivable Net Of Deferred Income LoansAndLeasesReceivableNetOfDeferredIncome	27053000000	USD
CY2021Q4	wal	Financing Receivable Cares Act Modification FinancingReceivableCARESActModification	152800000	USD
CY2021Q4	wal	Financing Receivable Troubled Debt Restructured Loans Number Of Outstanding Contracts FinancingReceivableTroubledDebtRestructuredLoansNumberOfOutstandingContracts	16	SecurityLoan
CY2021Q4	us-gaap	Financing Receivable Modifications Recorded Investment FinancingReceivableModificationsRecordedInvestment	20800000	USD
CY2020Q4	wal	Financing Receivable Troubled Debt Restructured Loans Number Of Outstanding Contracts FinancingReceivableTroubledDebtRestructuredLoansNumberOfOutstandingContracts	22	SecurityLoan
CY2020Q4	us-gaap	Financing Receivable Modifications Recorded Investment FinancingReceivableModificationsRecordedInvestment	61600000	USD
CY2021Q4	wal	Reserves Allocated To Customers Whose Loan Terms Modified In Troubled Debt Restructurings ReservesAllocatedToCustomersWhoseLoanTermsModifiedInTroubledDebtRestructurings	0	USD
CY2020Q4	wal	Reserves Allocated To Customers Whose Loan Terms Modified In Troubled Debt Restructurings ReservesAllocatedToCustomersWhoseLoanTermsModifiedInTroubledDebtRestructurings	2700000	USD
CY2021Q4	us-gaap	Loans And Leases Receivable Impaired Commitment To Lend LoansAndLeasesReceivableImpairedCommitmentToLend	0	USD
CY2020Q4	us-gaap	Loans And Leases Receivable Impaired Commitment To Lend LoansAndLeasesReceivableImpairedCommitmentToLend	600000	USD
CY2021	us-gaap	Financing Receivable Modifications Number Of Contracts2 FinancingReceivableModificationsNumberOfContracts2	9	SecurityLoan
CY2021	us-gaap	Financing Receivable Modifications Post Modification Recorded Investment2 FinancingReceivableModificationsPostModificationRecordedInvestment2	12500000	USD
CY2020	us-gaap	Financing Receivable Modifications Number Of Contracts2 FinancingReceivableModificationsNumberOfContracts2	17	SecurityLoan
CY2020	us-gaap	Financing Receivable Modifications Post Modification Recorded Investment2 FinancingReceivableModificationsPostModificationRecordedInvestment2	37300000	USD
CY2021	us-gaap	Financing Receivable Modifications Subsequent Default Number Of Contracts1 FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1	1	SecurityLoan
CY2021	us-gaap	Financing Receivable Modifications Subsequent Default Recorded Investment1 FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1	2100000	USD
CY2021	us-gaap	Financing Receivables Impaired Troubled Debt Restructuring Write Down FinancingReceivablesImpairedTroubledDebtRestructuringWriteDown	2000000	USD
CY2020	us-gaap	Financing Receivable Modifications Subsequent Default Number Of Contracts1 FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1	3	SecurityLoan
CY2020	us-gaap	Financing Receivable Modifications Subsequent Default Recorded Investment1 FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1	5800000	USD
CY2021Q4	us-gaap	Loans And Leases Receivable Collateral For Secured Borrowings LoansAndLeasesReceivableCollateralForSecuredBorrowings	226800000	USD
CY2020Q4	us-gaap	Loans And Leases Receivable Collateral For Secured Borrowings LoansAndLeasesReceivableCollateralForSecuredBorrowings	196200000	USD
CY2020Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	278900000	USD
CY2021	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	20500000	USD
CY2021	us-gaap	Financing Receivable Allowance For Credit Losses Write Offs FinancingReceivableAllowanceForCreditLossesWriteOffs	11600000	USD
CY2021	us-gaap	Financing Receivable Allowance For Credit Losses Recovery FinancingReceivableAllowanceForCreditLossesRecovery	5700000	USD
CY2021Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	252500000	USD
CY2020Q1	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	186900000	USD
CY2020	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	106500000	USD
CY2020	us-gaap	Financing Receivable Allowance For Credit Losses Write Offs FinancingReceivableAllowanceForCreditLossesWriteOffs	20400000	USD
CY2020	us-gaap	Financing Receivable Allowance For Credit Losses Recovery FinancingReceivableAllowanceForCreditLossesRecovery	5900000	USD
CY2020Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	278900000	USD
CY2021Q4	us-gaap	Interest Receivable InterestReceivable	197600000	USD
CY2020Q4	us-gaap	Interest Receivable InterestReceivable	142100000	USD
CY2020Q4	us-gaap	Off Balance Sheet Credit Loss Liability OffBalanceSheetCreditLossLiability	37000000.0	USD
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CY2021	us-gaap	Off Balance Sheet Credit Loss Liability Change In Method Credit Loss Expense Reversal OffBalanceSheetCreditLossLiabilityChangeInMethodCreditLossExpenseReversal	600000	USD
CY2020	us-gaap	Off Balance Sheet Credit Loss Liability Change In Method Credit Loss Expense Reversal OffBalanceSheetCreditLossLiabilityChangeInMethodCreditLossExpenseReversal	12900000	USD
CY2021Q4	us-gaap	Off Balance Sheet Credit Loss Liability OffBalanceSheetCreditLossLiability	37600000	USD
CY2020Q4	us-gaap	Off Balance Sheet Credit Loss Liability OffBalanceSheetCreditLossLiability	37000000.0	USD
CY2021Q4	us-gaap	Financing Receivable Collectively Evaluated For Impairment FinancingReceivableCollectivelyEvaluatedForImpairment	38812300000	USD
CY2021Q4	us-gaap	Financing Receivable Individually Evaluated For Impairment FinancingReceivableIndividuallyEvaluatedForImpairment	263100000	USD
CY2021Q4	us-gaap	Loans And Leases Receivable Net Of Deferred Income LoansAndLeasesReceivableNetOfDeferredIncome	39075400000	USD
CY2021Q4	us-gaap	Financing Receivable Allowance For Credit Losses Collectively Evaluated For Impairment FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment	236400000	USD
CY2021Q4	us-gaap	Financing Receivable Allowance For Credit Losses Individually Evaluated For Impairment1 FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1	16100000	USD
CY2021Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	252500000	USD
CY2020Q4	us-gaap	Financing Receivable Collectively Evaluated For Impairment FinancingReceivableCollectivelyEvaluatedForImpairment	26787400000	USD
CY2020Q4	us-gaap	Financing Receivable Individually Evaluated For Impairment FinancingReceivableIndividuallyEvaluatedForImpairment	265600000	USD
CY2020Q4	us-gaap	Loans And Leases Receivable Net Of Deferred Income LoansAndLeasesReceivableNetOfDeferredIncome	27053000000	USD
CY2020Q4	us-gaap	Financing Receivable Allowance For Credit Losses Collectively Evaluated For Impairment FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment	267700000	USD
CY2020Q4	us-gaap	Financing Receivable Allowance For Credit Losses Individually Evaluated For Impairment1 FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1	11200000	USD
CY2020Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	278900000	USD
CY2021	us-gaap	Financing Receivable Significant Purchases FinancingReceivableSignificantPurchases	12300000000	USD
CY2020	us-gaap	Financing Receivable Significant Purchases FinancingReceivableSignificantPurchases	2700000000	USD
CY2021	us-gaap	Financing Receivable Significant Sales FinancingReceivableSignificantSales	551200000	USD
CY2021	us-gaap	Loans And Leases Receivable Gain Loss On Sales Net LoansAndLeasesReceivableGainLossOnSalesNet	7200000	USD
CY2020	us-gaap	Financing Receivable Significant Sales FinancingReceivableSignificantSales	77300000	USD
CY2020	us-gaap	Loans And Leases Receivable Gain Loss On Sales Net LoansAndLeasesReceivableGainLossOnSalesNet	1700000	USD
CY2020Q4	us-gaap	Servicing Asset At Fair Value Amount ServicingAssetAtFairValueAmount	0	USD
CY2021Q2	wal	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Servicing Assets BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedServicingAssets	1347000000	USD
CY2021	us-gaap	Servicing Asset At Fair Value Additions ServicingAssetAtFairValueAdditions	763800000	USD
CY2021	us-gaap	Servicing Asset At Fair Value Disposals ServicingAssetAtFairValueDisposals	1270700000	USD
CY2021	us-gaap	Servicing Asset At Fair Value Changes In Fair Value Resulting From Changes In Valuation Inputs Or Changes In Assumptions ServicingAssetAtFairValueChangesInFairValueResultingFromChangesInValuationInputsOrChangesInAssumptions	-2500000	USD
CY2021	us-gaap	Servicing Asset At Fair Value Other Changes In Fair Value ServicingAssetAtFairValueOtherChangesInFairValue	-139600000	USD
CY2021Q4	us-gaap	Servicing Asset At Fair Value Amount ServicingAssetAtFairValueAmount	698000000.0	USD
CY2021Q4	us-gaap	Continuing Involvement With Transferred Financial Assets Principal Amount Outstanding ContinuingInvolvementWithTransferredFinancialAssetsPrincipalAmountOutstanding	54347600000	USD
CY2021	wal	Msr Sales Upb Of Underlying Loans MSRSalesUPBOfUnderlyingLoans	97200000000	USD
CY2021Q4	wal	Msr Loan Sales Receivable MSRLoanSalesReceivable	82500000	USD
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CY2021Q4	us-gaap	Servicing Asset At Fair Value Amount ServicingAssetAtFairValueAmount	698000000.0	USD
CY2021Q4	wal	Sensitivity Analysis Of Fair Value Transferors Interests In Transferred Financial Assets Impact Of50 Basis Point Adverse Interest Rate Change SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsImpactOf50BasisPointAdverseInterestRateChange	-61600000	USD
CY2021Q4	wal	Sensitivity Analysis Of Fair Value Transferors Interests In Transferred Financial Assets Impact Of50 Basis Point Favorable Interest Rate Change SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsImpactOf50BasisPointFavorableInterestRateChange	39900000	USD
CY2021Q4	wal	Sensitivity Analysis Of Fair Value Transferors Interests In Transferred Financial Assets Impact Of50 Basis Point Discount Rate Increase SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsImpactOf50BasisPointDiscountRateIncrease	13300000	USD
CY2021Q4	wal	Sensitivity Analysis Of Fair Value Transferors Interests In Transferred Financial Assets Impact Of50 Basis Point Discount Rate Decrease SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsImpactOf50BasisPointDiscountRateDecrease	13800000	USD
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CY2021Q4	wal	Sensitivity Analysis Of Fair Value Transferors Interests In Transferred Financial Assets Impact Of10 Percent Increase Cost Of Service SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsImpactOf10PercentIncreaseCostOfService	9600000	USD
CY2021Q4	wal	Sensitivity Analysis Of Fair Value Transferors Interests In Transferred Financial Assets Impact Of10 Percent Decrease Cost Of Service SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsImpactOf10PercentDecreaseCostOfService	9600000	USD
CY2021Q4	us-gaap	Buildings And Improvements Gross BuildingsAndImprovementsGross	91600000	USD
CY2020Q4	us-gaap	Buildings And Improvements Gross BuildingsAndImprovementsGross	92000000.0	USD
CY2021Q4	us-gaap	Land And Land Improvements LandAndLandImprovements	32400000	USD
CY2020Q4	us-gaap	Land And Land Improvements LandAndLandImprovements	33000000.0	USD
CY2021Q4	us-gaap	Furniture And Fixtures Gross FurnitureAndFixturesGross	99600000	USD
CY2020Q4	us-gaap	Furniture And Fixtures Gross FurnitureAndFixturesGross	68200000	USD
CY2021Q4	us-gaap	Leasehold Improvements Gross LeaseholdImprovementsGross	41500000	USD
CY2020Q4	us-gaap	Leasehold Improvements Gross LeaseholdImprovementsGross	29700000	USD
CY2021Q4	us-gaap	Construction In Progress Gross ConstructionInProgressGross	42700000	USD
CY2020Q4	us-gaap	Construction In Progress Gross ConstructionInProgressGross	17400000	USD
CY2021Q4	us-gaap	Property Plant And Equipment Gross PropertyPlantAndEquipmentGross	307800000	USD
CY2020Q4	us-gaap	Property Plant And Equipment Gross PropertyPlantAndEquipmentGross	240300000	USD
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CY2021Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	181900000	USD
CY2020Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	134100000	USD
CY2021	us-gaap	Depreciation Depreciation	20700000	USD
CY2020	us-gaap	Depreciation Depreciation	15200000	USD
CY2019	us-gaap	Depreciation Depreciation	13500000	USD
CY2021Q4	us-gaap	Operating Lease Right Of Use Asset OperatingLeaseRightOfUseAsset	133000000	USD
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CY2021Q4	us-gaap	Lessee Operating Lease Liability Payments Due Next Twelve Months LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths	15100000	USD
CY2021Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Two LesseeOperatingLeaseLiabilityPaymentsDueYearTwo	20700000	USD
CY2021Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Three LesseeOperatingLeaseLiabilityPaymentsDueYearThree	22700000	USD
CY2021Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Four LesseeOperatingLeaseLiabilityPaymentsDueYearFour	18300000	USD
CY2021Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Five LesseeOperatingLeaseLiabilityPaymentsDueYearFive	19300000	USD
CY2021Q4	us-gaap	Lessee Operating Lease Liability Payments Due After Year Five LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive	60200000	USD
CY2021Q4	us-gaap	Lessee Operating Lease Liability Payments Due LesseeOperatingLeaseLiabilityPaymentsDue	156300000	USD
CY2021Q4	us-gaap	Lessee Operating Lease Liability Undiscounted Excess Amount LesseeOperatingLeaseLiabilityUndiscountedExcessAmount	13500000	USD
CY2021Q4	us-gaap	Operating Lease Liability OperatingLeaseLiability	142800000	USD
CY2021Q4	wal	Lesseeoperatingleaseleasesnotyetcommencedaggregatedcommitment Lesseeoperatingleaseleasesnotyetcommencedaggregatedcommitment	36900000	USD
CY2021	us-gaap	Lease Cost LeaseCost	18800000	USD
CY2021	us-gaap	Variable Lease Cost VariableLeaseCost	3800000	USD
CY2020	us-gaap	Lease Cost LeaseCost	14000000	USD
CY2020	us-gaap	Variable Lease Cost VariableLeaseCost	3900000	USD
CY2019	us-gaap	Lease Cost LeaseCost	12900000	USD
CY2019	us-gaap	Variable Lease Cost VariableLeaseCost	4000000	USD
CY2021	us-gaap	Operating Lease Payments OperatingLeasePayments	16300000	USD
CY2020	us-gaap	Operating Lease Payments OperatingLeasePayments	13000000.0	USD
CY2019	us-gaap	Operating Lease Payments OperatingLeasePayments	12400000	USD
CY2021	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	76700000	USD
CY2020	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	11800000	USD
CY2019	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	43700000	USD
CY2021Q4	us-gaap	Goodwill Goodwill	491300000	USD
CY2020Q4	us-gaap	Goodwill Goodwill	289900000	USD
CY2021Q4	us-gaap	Finite Lived Intangible Assets Gross FiniteLivedIntangibleAssetsGross	158100000	USD
CY2021Q4	us-gaap	Finite Lived Intangible Assets Accumulated Amortization FiniteLivedIntangibleAssetsAccumulatedAmortization	15000000.0	USD
CY2021Q4	us-gaap	Finite Lived Intangible Assets Net FiniteLivedIntangibleAssetsNet	143100000	USD
CY2020Q4	us-gaap	Finite Lived Intangible Assets Gross FiniteLivedIntangibleAssetsGross	17100000	USD
CY2020Q4	us-gaap	Finite Lived Intangible Assets Accumulated Amortization FiniteLivedIntangibleAssetsAccumulatedAmortization	8900000	USD
CY2020Q4	us-gaap	Finite Lived Intangible Assets Net FiniteLivedIntangibleAssetsNet	8200000	USD
CY2021Q4	wal	Indefinite Lived Trade Name Gross IndefiniteLivedTradeNameGross	400000	USD
CY2021Q4	wal	Trade Name Impaired Accumulated Impairment Loss TradeNameImpairedAccumulatedImpairmentLoss	0	USD
CY2021Q4	us-gaap	Indefinite Lived Trade Names IndefiniteLivedTradeNames	400000	USD
CY2020Q4	wal	Indefinite Lived Trade Name Gross IndefiniteLivedTradeNameGross	400000	USD
CY2020Q4	wal	Trade Name Impaired Accumulated Impairment Loss TradeNameImpairedAccumulatedImpairmentLoss	0	USD
CY2020Q4	us-gaap	Indefinite Lived Trade Names IndefiniteLivedTradeNames	400000	USD
CY2021	us-gaap	Acquired Finite Lived Intangible Assets Weighted Average Useful Life AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife	P26Y2M12D
CY2021	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	6100000	USD
CY2020	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	1600000	USD
CY2019	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	1600000	USD
CY2021Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Next Twelve Months FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths	7500000	USD
CY2021Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Two FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo	7400000	USD
CY2021Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Three FiniteLivedIntangibleAssetsAmortizationExpenseYearThree	7400000	USD
CY2021Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Four FiniteLivedIntangibleAssetsAmortizationExpenseYearFour	6600000	USD
CY2021Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Five FiniteLivedIntangibleAssetsAmortizationExpenseYearFive	5700000	USD
CY2021Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense After Year Five FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive	108500000	USD
CY2021Q4	us-gaap	Finite Lived Intangible Assets Net FiniteLivedIntangibleAssetsNet	143100000	USD
CY2021Q4	us-gaap	Senior Notes SeniorNotes	317900000	USD
CY2021Q4	us-gaap	Noninterest Bearing Deposit Liabilities NoninterestBearingDepositLiabilities	21353400000	USD
CY2020Q4	us-gaap	Noninterest Bearing Deposit Liabilities NoninterestBearingDepositLiabilities	13463300000	USD
CY2021Q4	us-gaap	Interest Bearing Domestic Deposit Demand InterestBearingDomesticDepositDemand	6924000000	USD
CY2020Q4	us-gaap	Interest Bearing Domestic Deposit Demand InterestBearingDomesticDepositDemand	4396400000	USD
CY2021Q4	us-gaap	Deposits Savings Deposits DepositsSavingsDeposits	17278600000	USD
CY2020Q4	us-gaap	Deposits Savings Deposits DepositsSavingsDeposits	12413400000	USD
CY2021Q4	wal	Time Deposits250000ormore TimeDeposits250000ormore	523000000.0	USD
CY2020Q4	wal	Time Deposits250000ormore TimeDeposits250000ormore	602000000.0	USD
CY2021Q4	wal	Time Deposits Lessthan250000 TimeDepositsLessthan250000	1533000000	USD
CY2020Q4	wal	Time Deposits Lessthan250000 TimeDepositsLessthan250000	1055400000	USD
CY2021Q4	us-gaap	Deposits Deposits	47612000000	USD
CY2020Q4	us-gaap	Deposits Deposits	31930500000	USD
CY2021Q4	us-gaap	Time Deposit Maturities Year One TimeDepositMaturitiesYearOne	1932400000	USD
CY2021Q4	us-gaap	Time Deposit Maturities Year Two TimeDepositMaturitiesYearTwo	102200000	USD
CY2021Q4	us-gaap	Time Deposit Maturities Year Three TimeDepositMaturitiesYearThree	17400000	USD
CY2021Q4	us-gaap	Time Deposit Maturities Year Four TimeDepositMaturitiesYearFour	2900000	USD
CY2021Q4	us-gaap	Time Deposit Maturities Year Five TimeDepositMaturitiesYearFive	1100000	USD
CY2021Q4	us-gaap	Time Deposits TimeDeposits	2056000000	USD
CY2021Q4	wal	Certificatesof Deposit Cdars CertificatesofDepositCDARS	729200000	USD
CY2020Q4	wal	Certificatesof Deposit Cdars CertificatesofDepositCDARS	496400000	USD
CY2021Q4	wal	Deposits Ics DepositsICS	1800000000	USD
CY2020Q4	wal	Deposits Ics DepositsICS	1300000000	USD
CY2021Q4	us-gaap	Deposits Wholesale DepositsWholesale	1800000000	USD
CY2020Q4	us-gaap	Deposits Wholesale DepositsWholesale	554800000	USD
CY2021Q4	wal	Deposits Earnings Credit DepositsEarningsCredit	10800000000	USD
CY2020Q4	wal	Deposits Earnings Credit DepositsEarningsCredit	5900000000	USD
CY2021	wal	Depositscostsdepositswithearningscredits Depositscostsdepositswithearningscredits	27400000	USD
CY2020	wal	Depositscostsdepositswithearningscredits Depositscostsdepositswithearningscredits	17000000	USD
CY2021Q4	us-gaap	Federal Funds Purchased FederalFundsPurchased	675000000.0	USD
CY2020Q4	us-gaap	Federal Funds Purchased FederalFundsPurchased	0	USD
CY2021Q4	us-gaap	Federal Home Loan Bank Advances Maturities Summary Due Within One Year Of Balance Sheet Date FederalHomeLoanBankAdvancesMaturitiesSummaryDueWithinOneYearOfBalanceSheetDate	0	USD
CY2020Q4	us-gaap	Federal Home Loan Bank Advances Maturities Summary Due Within One Year Of Balance Sheet Date FederalHomeLoanBankAdvancesMaturitiesSummaryDueWithinOneYearOfBalanceSheetDate	5000000.0	USD
CY2021Q4	us-gaap	Securities Sold Under Agreements To Repurchase SecuritiesSoldUnderAgreementsToRepurchase	16600000	USD
CY2020Q4	us-gaap	Securities Sold Under Agreements To Repurchase SecuritiesSoldUnderAgreementsToRepurchase	16000000.0	USD
CY2021Q4	us-gaap	Other Short Term Borrowings OtherShortTermBorrowings	35300000	USD
CY2020Q4	us-gaap	Other Short Term Borrowings OtherShortTermBorrowings	0	USD
CY2021Q4	us-gaap	Short Term Borrowings ShortTermBorrowings	726900000	USD
CY2020Q4	us-gaap	Short Term Borrowings ShortTermBorrowings	21000000.0	USD
CY2020Q4	us-gaap	Senior Notes SeniorNotes	0	USD
CY2021Q4	us-gaap	Notes Payable NotesPayable	457100000	USD
CY2020Q4	us-gaap	Notes Payable NotesPayable	0	USD
CY2021Q4	us-gaap	Long Term Debt LongTermDebt	775000000.0	USD
CY2020Q4	us-gaap	Long Term Debt LongTermDebt	0	USD
CY2021Q4	us-gaap	Other Borrowings OtherBorrowings	1501900000	USD
CY2020Q4	us-gaap	Other Borrowings OtherBorrowings	21000000.0	USD
CY2021Q4	us-gaap	Federal Funds Purchased FederalFundsPurchased	675000000	USD
CY2020Q4	us-gaap	Federal Funds Purchased FederalFundsPurchased	0	USD
CY2021Q4	us-gaap	Federal Home Loan Bank Advances Maturities Summary Due Within One Year Of Balance Sheet Date FederalHomeLoanBankAdvancesMaturitiesSummaryDueWithinOneYearOfBalanceSheetDate	0	USD
CY2021Q4	us-gaap	Federal Home Loan Bank Advances Maturities Summary Due Within One Year Of Balance Sheet Date FederalHomeLoanBankAdvancesMaturitiesSummaryDueWithinOneYearOfBalanceSheetDate	0	USD
CY2021Q4	us-gaap	Securities Sold Under Agreements To Repurchase SecuritiesSoldUnderAgreementsToRepurchase	16600000	USD
CY2020Q4	us-gaap	Securities Sold Under Agreements To Repurchase SecuritiesSoldUnderAgreementsToRepurchase	16000000	USD
CY2021Q4	us-gaap	Other Short Term Borrowings OtherShortTermBorrowings	35300000	USD
CY2021Q4	us-gaap	Senior Notes SeniorNotes	317900000	USD
CY2021Q4	us-gaap	Notes Payable NotesPayable	457100000	USD
CY2021Q4	us-gaap	Subordinated Long Term Debt SubordinatedLongTermDebt	815100000	USD
CY2020Q4	us-gaap	Subordinated Long Term Debt SubordinatedLongTermDebt	469800000	USD
CY2021Q4	wal	Unrealizedgainorlossonjuniorsubordinateddebtcarriedatfairvalue Unrealizedgainorlossonjuniorsubordinateddebtcarriedatfairvalue	900000	USD
CY2020Q4	wal	Unrealizedgainorlossonjuniorsubordinateddebtcarriedatfairvalue Unrealizedgainorlossonjuniorsubordinateddebtcarriedatfairvalue	600000	USD
CY2021Q4	wal	Business Combination Fair Market Value Adjustmenton Junior Subordinated Debenture Owedto Unconsolidated Subsidiary Trust BusinessCombinationFairMarketValueAdjustmentonJuniorSubordinatedDebentureOwedtoUnconsolidatedSubsidiaryTrust	4200000	USD
CY2020Q4	wal	Business Combination Fair Market Value Adjustmenton Junior Subordinated Debenture Owedto Unconsolidated Subsidiary Trust BusinessCombinationFairMarketValueAdjustmentonJuniorSubordinatedDebentureOwedtoUnconsolidatedSubsidiaryTrust	4500000	USD
CY2021Q4	us-gaap	Junior Subordinated Debenture Owed To Unconsolidated Subsidiary Trust JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust	80700000	USD
CY2020Q4	us-gaap	Junior Subordinated Debenture Owed To Unconsolidated Subsidiary Trust JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust	78900000	USD
CY2021Q4	us-gaap	Junior Subordinated Debenture Owed To Unconsolidated Subsidiary Trust JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust	80700000	USD
CY2020Q4	us-gaap	Junior Subordinated Debenture Owed To Unconsolidated Subsidiary Trust JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust	78900000	USD
CY2021Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Authorized ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized	11800000	shares
CY2021Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Available For Grant ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant	3000000	shares
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Number ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	1000000.0	shares
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue	50.12
CY2019Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Number ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	1000000.0	shares
CY2019Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue	49.98
CY2021	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Grants In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod	400000	shares
CY2021	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Grants In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue	83.56
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Grants In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod	400000	shares
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Grants In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue	51.53
CY2021	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod	400000	shares
CY2021	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue	53.50
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod	400000	shares
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue	51.86
CY2021	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Forfeited In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod	100000	shares
CY2021	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Forfeitures Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue	59.24
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Forfeited In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod	0.0	shares
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Forfeitures Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue	49.79
CY2021Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Number ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	900000	shares
CY2021Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue	63.53
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Number ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	1000000.0	shares
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue	50.12
CY2021Q4	us-gaap	Employee Service Share Based Compensation Nonvested Awards Total Compensation Cost Not Yet Recognized Share Based Awards Other Than Options EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions	28000000	USD
CY2021	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Outstanding Weighted Average Remaining Contractual Terms ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageRemainingContractualTerms	P2Y
CY2021	us-gaap	Preferred Stock Dividends Per Share Cash Paid PreferredStockDividendsPerShareCashPaid	0.29
CY2021	us-gaap	Adjustments To Additional Paid In Capital Stock Issued Issuance Costs AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts	2300000	USD
CY2020Q4	us-gaap	Stock Repurchase Program Authorized Amount1 StockRepurchaseProgramAuthorizedAmount1	250000000	USD
CY2020	us-gaap	Stock Repurchased And Retired During Period Shares StockRepurchasedAndRetiredDuringPeriodShares	2100000	shares
CY2020	wal	Weighted Average Selling Price Per Share WeightedAverageSellingPricePerShare	34.65
CY2020	us-gaap	Stock Repurchased And Retired During Period Value StockRepurchasedAndRetiredDuringPeriodValue	71600000	USD
	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	0.25
	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	0.35
CY2020	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	0.25
CY2021	us-gaap	Shares Paid For Tax Withholding For Share Based Compensation SharesPaidForTaxWithholdingForShareBasedCompensation	180607	shares
CY2021	us-gaap	Treasury Stock Acquired Average Cost Per Share TreasuryStockAcquiredAverageCostPerShare	86.63
CY2020	us-gaap	Shares Paid For Tax Withholding For Share Based Compensation SharesPaidForTaxWithholdingForShareBasedCompensation	165489	shares
CY2020	us-gaap	Treasury Stock Acquired Average Cost Per Share TreasuryStockAcquiredAverageCostPerShare	50.80
CY2019	us-gaap	Shares Paid For Tax Withholding For Share Based Compensation SharesPaidForTaxWithholdingForShareBasedCompensation	210657	shares
CY2019	us-gaap	Treasury Stock Acquired Average Cost Per Share TreasuryStockAcquiredAverageCostPerShare	45.80
CY2018Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-33600000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Before Reclassifications Net Of Tax OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax	61000000.0	USD
CY2019	us-gaap	Reclassification From Accumulated Other Comprehensive Income Current Period Net Of Tax ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax	2400000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	58600000	USD
CY2019Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	25000000.0	USD
CY2020	us-gaap	Other Comprehensive Income Loss Before Reclassifications Net Of Tax OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax	67500000	USD
CY2020	us-gaap	Reclassification From Accumulated Other Comprehensive Income Current Period Net Of Tax ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax	200000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	67300000	USD
CY2020Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	92300000	USD
CY2021	us-gaap	Other Comprehensive Income Loss Before Reclassifications Net Of Tax OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax	-70200000	USD
CY2021	us-gaap	Reclassification From Accumulated Other Comprehensive Income Current Period Net Of Tax ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax	6400000	USD
CY2021	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	-76600000	USD
CY2021Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	15700000	USD
CY2021	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax	8500000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax	200000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax	3100000	USD
CY2021	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesTax	2100000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesTax	0	USD
CY2021	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax	6400000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax	200000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax	2400000	USD
CY2021Q4	us-gaap	Hedged Asset Fair Value Hedge HedgedAssetFairValueHedge	1390700000	USD
CY2021Q4	us-gaap	Hedged Asset Fair Value Hedge Cumulative Increase Decrease HedgedAssetFairValueHedgeCumulativeIncreaseDecrease	38500000	USD
CY2020Q4	us-gaap	Hedged Asset Fair Value Hedge HedgedAssetFairValueHedge	1587100000	USD
CY2020Q4	us-gaap	Hedged Asset Fair Value Hedge Cumulative Increase Decrease HedgedAssetFairValueHedgeCumulativeIncreaseDecrease	85500000	USD
CY2021Q4	us-gaap	Hedged Liability Fair Value Hedge HedgedLiabilityFairValueHedge	0	USD
CY2021Q4	us-gaap	Hedged Liability Fair Value Hedge Cumulative Increase Decrease HedgedLiabilityFairValueHedgeCumulativeIncreaseDecrease	0	USD
CY2020Q4	us-gaap	Hedged Liability Fair Value Hedge HedgedLiabilityFairValueHedge	247600000	USD
CY2020Q4	us-gaap	Hedged Liability Fair Value Hedge Cumulative Increase Decrease HedgedLiabilityFairValueHedgeCumulativeIncreaseDecrease	-2700000	USD
CY2021Q4	us-gaap	Hedged Asset Fair Value Hedge Last Of Layer Amount HedgedAssetFairValueHedgeLastOfLayerAmount	880000000	USD
CY2021Q4	us-gaap	Prepayable Financial Asset Closed Portfolio Last Of Layer Amortized Cost PrepayableFinancialAssetClosedPortfolioLastOfLayerAmortizedCost	1400000000	USD
CY2020Q4	us-gaap	Prepayable Financial Asset Closed Portfolio Last Of Layer Amortized Cost PrepayableFinancialAssetClosedPortfolioLastOfLayerAmortizedCost	1900000000	USD
CY2021Q4	us-gaap	Hedged Asset Fair Value Hedge Last Of Layer Cumulative Increase Decrease HedgedAssetFairValueHedgeLastOfLayerCumulativeIncreaseDecrease	15700000	USD
CY2020Q4	us-gaap	Hedged Asset Fair Value Hedge Last Of Layer Cumulative Increase Decrease HedgedAssetFairValueHedgeLastOfLayerCumulativeIncreaseDecrease	600000	USD
CY2021Q4	us-gaap	Derivative Asset Collateral Obligation To Return Cash Offset DerivativeAssetCollateralObligationToReturnCashOffset	1200000	USD
CY2021Q4	us-gaap	Derivative Asset Collateral Obligation To Return Cash Offset DerivativeAssetCollateralObligationToReturnCashOffset	1200000	USD
CY2021Q4	wal	Derivative Netting Adjustments Assets DerivativeNettingAdjustmentsAssets	-28400000	USD
CY2021Q4	wal	Derivative Netting Adjustments Assets DerivativeNettingAdjustmentsAssets	-28400000	USD
CY2020Q4	wal	Derivative Netting Adjustments Assets DerivativeNettingAdjustmentsAssets	-600000	USD
CY2020Q4	wal	Derivative Netting Adjustments Assets DerivativeNettingAdjustmentsAssets	-600000	USD
CY2021Q4	us-gaap	Derivative Fair Value Of Derivative Asset DerivativeFairValueOfDerivativeAsset	38400000	USD
CY2020	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	100200000	shares
CY2021Q4	wal	Derivative Netting Adjustments Assets DerivativeNettingAdjustmentsAssets	-28400000	USD
CY2021Q4	us-gaap	Derivative Fair Value Of Derivative Asset Amount Offset Against Collateral DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral	10000000.0	USD
CY2020Q4	us-gaap	Derivative Fair Value Of Derivative Asset DerivativeFairValueOfDerivativeAsset	3300000	USD
CY2020Q4	wal	Derivative Netting Adjustments Assets DerivativeNettingAdjustmentsAssets	-600000	USD
CY2020Q4	us-gaap	Derivative Fair Value Of Derivative Asset Amount Offset Against Collateral DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral	2700000	USD
CY2019Q4	us-gaap	Derivative Fair Value Of Derivative Asset DerivativeFairValueOfDerivativeAsset	1800000	USD
CY2019Q4	wal	Derivative Netting Adjustments Assets DerivativeNettingAdjustmentsAssets	0	USD
CY2019Q4	us-gaap	Derivative Fair Value Of Derivative Asset Amount Offset Against Collateral DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral	1800000	USD
CY2021Q4	us-gaap	Derivative Liability Collateral Right To Reclaim Cash Offset DerivativeLiabilityCollateralRightToReclaimCashOffset	6500000	USD
CY2021Q4	us-gaap	Derivative Liability Collateral Right To Reclaim Cash Offset DerivativeLiabilityCollateralRightToReclaimCashOffset	6500000	USD
CY2021Q4	wal	Derivative Netting Adjustments Liabilities DerivativeNettingAdjustmentsLiabilities	28400000	USD
CY2021Q4	wal	Derivative Netting Adjustments Liabilities DerivativeNettingAdjustmentsLiabilities	28400000	USD
CY2020Q4	wal	Derivative Netting Adjustments Liabilities DerivativeNettingAdjustmentsLiabilities	600000	USD
CY2020Q4	wal	Derivative Netting Adjustments Liabilities DerivativeNettingAdjustmentsLiabilities	600000	USD
CY2021Q4	us-gaap	Derivative Fair Value Of Derivative Liability DerivativeFairValueOfDerivativeLiability	96300000	USD
CY2021Q4	wal	Derivative Netting Adjustments Liabilities DerivativeNettingAdjustmentsLiabilities	28400000	USD
CY2021Q4	us-gaap	Derivative Fair Value Of Derivative Liability Amount Offset Against Collateral DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral	67900000	USD
CY2020Q4	us-gaap	Derivative Fair Value Of Derivative Liability DerivativeFairValueOfDerivativeLiability	86100000	USD
CY2020Q4	wal	Derivative Netting Adjustments Liabilities DerivativeNettingAdjustmentsLiabilities	600000	USD
CY2020Q4	us-gaap	Derivative Fair Value Of Derivative Liability Amount Offset Against Collateral DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral	85500000	USD
CY2019Q4	us-gaap	Derivative Fair Value Of Derivative Liability DerivativeFairValueOfDerivativeLiability	55500000	USD
CY2019Q4	wal	Derivative Netting Adjustments Liabilities DerivativeNettingAdjustmentsLiabilities	0	USD
CY2019Q4	us-gaap	Derivative Fair Value Of Derivative Liability Amount Offset Against Collateral DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral	55500000	USD
CY2021Q4	us-gaap	Derivative Asset Not Subject To Master Netting Arrangement DerivativeAssetNotSubjectToMasterNettingArrangement	11800000	USD
CY2021Q4	us-gaap	Derivative Asset Not Subject To Master Netting Arrangement DerivativeAssetNotSubjectToMasterNettingArrangement	11800000	USD
CY2020Q4	us-gaap	Derivative Asset Not Subject To Master Netting Arrangement DerivativeAssetNotSubjectToMasterNettingArrangement	900000	USD
CY2020Q4	us-gaap	Derivative Asset Not Subject To Master Netting Arrangement DerivativeAssetNotSubjectToMasterNettingArrangement	900000	USD
CY2019Q4	us-gaap	Derivative Asset Not Subject To Master Netting Arrangement DerivativeAssetNotSubjectToMasterNettingArrangement	100000	USD
CY2019Q4	us-gaap	Derivative Asset Not Subject To Master Netting Arrangement DerivativeAssetNotSubjectToMasterNettingArrangement	100000	USD
CY2021Q4	us-gaap	Derivative Liability Not Subject To Master Netting Arrangement DerivativeLiabilityNotSubjectToMasterNettingArrangement	3500000	USD
CY2021Q4	us-gaap	Derivative Liability Not Subject To Master Netting Arrangement DerivativeLiabilityNotSubjectToMasterNettingArrangement	3500000	USD
CY2020Q4	us-gaap	Derivative Liability Not Subject To Master Netting Arrangement DerivativeLiabilityNotSubjectToMasterNettingArrangement	1400000	USD
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CY2020Q4	us-gaap	Common Equity Tier One Capital Required To Be Well Capitalized CommonEquityTierOneCapitalRequiredToBeWellCapitalized	0.065	USD
CY2020Q4	us-gaap	Capital Required For Capital Adequacy To Risk Weighted Assets CapitalRequiredForCapitalAdequacyToRiskWeightedAssets	0.080
CY2020Q4	us-gaap	Tier One Risk Based Capital Required For Capital Adequacy To Risk Weighted Assets TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets	0.060
CY2020Q4	us-gaap	Tier One Leverage Capital Required For Capital Adequacy To Average Assets TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets	0.040
CY2020Q4	us-gaap	Common Equity Tier One Capital Required For Capital Adequacy CommonEquityTierOneCapitalRequiredForCapitalAdequacy	0.045	USD
CY2021	us-gaap	Defined Contribution Plan Maximum Annual Contributions Per Employee Amount DefinedContributionPlanMaximumAnnualContributionsPerEmployeeAmount	19500	USD
CY2021	wal	Defined Contribution Plan Age Of Participants DefinedContributionPlanAgeOfParticipants	P50Y
CY2021	wal	Defined Contribution Plan Age Of Participants DefinedContributionPlanAgeOfParticipants	P50Y
CY2021	us-gaap	Defined Contribution Plan Employer Matching Contribution Percent Of Match DefinedContributionPlanEmployerMatchingContributionPercentOfMatch	1
CY2021	wal	Defined Contribution Plan Initial Percentage Of Discretionary Deferred Compensation DefinedContributionPlanInitialPercentageOfDiscretionaryDeferredCompensation	0.05
CY2021	us-gaap	Defined Contribution Plan Employer Discretionary Contribution Amount DefinedContributionPlanEmployerDiscretionaryContributionAmount	12000000	USD
CY2020	us-gaap	Defined Contribution Plan Employer Discretionary Contribution Amount DefinedContributionPlanEmployerDiscretionaryContributionAmount	7100000	USD
CY2019	us-gaap	Defined Contribution Plan Employer Discretionary Contribution Amount DefinedContributionPlanEmployerDiscretionaryContributionAmount	6200000	USD
CY2021Q4	us-gaap	Defined Benefit Plan Benefit Obligation DefinedBenefitPlanBenefitObligation	13100000	USD
CY2020Q4	us-gaap	Defined Benefit Plan Benefit Obligation DefinedBenefitPlanBenefitObligation	13600000	USD
CY2019	us-gaap	Defined Benefit Plan Net Periodic Benefit Cost DefinedBenefitPlanNetPeriodicBenefitCost	1100000	USD
CY2021	us-gaap	Defined Benefit Plan Net Periodic Benefit Cost DefinedBenefitPlanNetPeriodicBenefitCost	1100000	USD
CY2020	us-gaap	Defined Benefit Plan Net Periodic Benefit Cost DefinedBenefitPlanNetPeriodicBenefitCost	1100000	USD
CY2020Q4	us-gaap	Loans And Leases Receivable Related Parties LoansAndLeasesReceivableRelatedParties	3300000	USD
CY2019Q4	us-gaap	Loans And Leases Receivable Related Parties LoansAndLeasesReceivableRelatedParties	3800000	USD
CY2021	us-gaap	Loans And Leases Receivable Related Parties Additions LoansAndLeasesReceivableRelatedPartiesAdditions	0	USD
CY2020	us-gaap	Loans And Leases Receivable Related Parties Additions LoansAndLeasesReceivableRelatedPartiesAdditions	0	USD
CY2021	wal	Loansand Leases Receivable Advances Related Parties LoansandLeasesReceivableAdvancesRelatedParties	0	USD
CY2020	wal	Loansand Leases Receivable Advances Related Parties LoansandLeasesReceivableAdvancesRelatedParties	0	USD
CY2021	us-gaap	Repayment Of Notes Receivable From Related Parties RepaymentOfNotesReceivableFromRelatedParties	3300000	USD
CY2020	us-gaap	Repayment Of Notes Receivable From Related Parties RepaymentOfNotesReceivableFromRelatedParties	500000	USD
CY2021Q4	us-gaap	Loans And Leases Receivable Related Parties LoansAndLeasesReceivableRelatedParties	0	USD
CY2020Q4	us-gaap	Loans And Leases Receivable Related Parties LoansAndLeasesReceivableRelatedParties	3300000	USD
CY2021	us-gaap	Interest Income Related Party InterestIncomeRelatedParty	100000	USD
CY2020	us-gaap	Interest Income Related Party InterestIncomeRelatedParty	200000	USD
CY2019	us-gaap	Interest Income Related Party InterestIncomeRelatedParty	200000	USD
CY2021Q4	wal	Loanand Leases Receivable Commitment Outstanding Related Parties LoanandLeasesReceivableCommitmentOutstandingRelatedParties	7000000	USD
CY2020	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	506600000	USD
CY2019	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	499200000	USD
CY2020Q4	wal	Loanand Leases Receivable Commitment Outstanding Related Parties LoanandLeasesReceivableCommitmentOutstandingRelatedParties	10300000	USD
CY2021Q4	us-gaap	Related Party Deposit Liabilities RelatedPartyDepositLiabilities	101300000	USD
CY2020Q4	us-gaap	Related Party Deposit Liabilities RelatedPartyDepositLiabilities	156900000	USD
CY2021	us-gaap	Interest Expense Related Party InterestExpenseRelatedParty	200000	USD
CY2020	us-gaap	Interest Expense Related Party InterestExpenseRelatedParty	200000	USD
CY2019	us-gaap	Interest Expense Related Party InterestExpenseRelatedParty	300000	USD
CY2019	us-gaap	Related Party Transaction Expenses From Transactions With Related Party RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty	1000000	USD
CY2020	us-gaap	Related Party Transaction Expenses From Transactions With Related Party RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty	1000000	USD
CY2021	us-gaap	Related Party Transaction Expenses From Transactions With Related Party RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty	1000000	USD
CY2021	us-gaap	Preferred Stock Dividends Income Statement Impact PreferredStockDividendsIncomeStatementImpact	3500000	USD
CY2020	us-gaap	Preferred Stock Dividends Income Statement Impact PreferredStockDividendsIncomeStatementImpact	0	USD
CY2019	us-gaap	Preferred Stock Dividends Income Statement Impact PreferredStockDividendsIncomeStatementImpact	0	USD
CY2021	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	895700000	USD
CY2021Q4	wal	Cash Cash Equivalentsand Investment Securities CashCashEquivalentsandInvestmentSecurities	8057300000	USD
CY2021Q4	us-gaap	Loans Receivable Held For Sale Amount LoansReceivableHeldForSaleAmount	5635100000	USD
CY2021Q4	us-gaap	Loans And Leases Receivable Net Of Deferred Income LoansAndLeasesReceivableNetOfDeferredIncome	39075400000	USD
CY2021Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	252500000	USD
CY2021Q4	wal	Loansand Leases Receivable Including Heldfor Sale Net LoansandLeasesReceivableIncludingHeldforSaleNet	38822900000	USD
CY2021Q4	us-gaap	Other Foreclosed Assets OtherForeclosedAssets	11700000	USD
CY2021Q4	us-gaap	Intangible Assets Net Including Goodwill IntangibleAssetsNetIncludingGoodwill	634800000	USD
CY2021Q4	wal	Other Assets Segment OtherAssetsSegment	2820800000	USD
CY2021Q4	us-gaap	Assets Assets	55982600000	USD
CY2021Q4	us-gaap	Deposits Deposits	47612000000	USD
CY2021Q4	wal	Borrowingsand Qualifying Debt BorrowingsandQualifyingDebt	2381100000	USD
CY2021Q4	wal	Other Liabilities Segment OtherLiabilitiesSegment	1026900000	USD
CY2021Q4	us-gaap	Liabilities Liabilities	51020000000	USD
CY2021Q4	us-gaap	Stockholders Equity StockholdersEquity	4962600000	USD
CY2021Q4	us-gaap	Liabilities And Stockholders Equity LiabilitiesAndStockholdersEquity	55982600000	USD
CY2021Q4	wal	Excess Funds Providedby Usedin Segment Basis ExcessFundsProvidedbyUsedinSegmentBasis	0	USD
CY2020Q4	wal	Cash Cash Equivalentsand Investment Securities CashCashEquivalentsandInvestmentSecurities	8176500000	USD
CY2020Q4	us-gaap	Loans And Leases Receivable Net Of Deferred Income LoansAndLeasesReceivableNetOfDeferredIncome	27053000000	USD
CY2020Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	278900000	USD
CY2020Q4	wal	Loansand Leases Receivable Including Heldfor Sale Net LoansandLeasesReceivableIncludingHeldforSaleNet	26774100000	USD
CY2020Q4	us-gaap	Other Foreclosed Assets OtherForeclosedAssets	1400000	USD
CY2020Q4	us-gaap	Intangible Assets Net Including Goodwill IntangibleAssetsNetIncludingGoodwill	298500000	USD
CY2020Q4	wal	Other Assets Segment OtherAssetsSegment	1210500000	USD
CY2020Q4	us-gaap	Assets Assets	36461000000	USD
CY2020Q4	us-gaap	Deposits Deposits	31930500000	USD
CY2020Q4	wal	Borrowingsand Qualifying Debt BorrowingsandQualifyingDebt	553700000	USD
CY2020Q4	wal	Other Liabilities Segment OtherLiabilitiesSegment	563300000	USD
CY2020Q4	us-gaap	Liabilities Liabilities	33047500000	USD
CY2020Q4	us-gaap	Stockholders Equity StockholdersEquity	3413500000	USD
CY2020Q4	us-gaap	Liabilities And Stockholders Equity LiabilitiesAndStockholdersEquity	36461000000	USD
CY2020Q4	wal	Excess Funds Providedby Usedin Segment Basis ExcessFundsProvidedbyUsedinSegmentBasis	0	USD
CY2021	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	1548800000	USD
CY2021	us-gaap	Provision For Loan Lease And Other Losses ProvisionForLoanLeaseAndOtherLosses	21400000	USD
CY2021	us-gaap	Interest Income Expense After Provision For Loan Loss InterestIncomeExpenseAfterProvisionForLoanLoss	1570200000	USD
CY2021	us-gaap	Noninterest Income NoninterestIncome	404200000	USD
CY2021	us-gaap	Noninterest Expense NoninterestExpense	851400000	USD
CY2021	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	1123000000	USD
CY2021	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	223800000	USD
CY2021	us-gaap	Net Income Loss NetIncomeLoss	899200000	USD
CY2020	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	1166900000	USD
CY2020	us-gaap	Provision For Loan Lease And Other Losses ProvisionForLoanLeaseAndOtherLosses	123600000	USD
CY2020	us-gaap	Interest Income Expense After Provision For Loan Loss InterestIncomeExpenseAfterProvisionForLoanLoss	1043300000	USD
CY2020	us-gaap	Noninterest Income NoninterestIncome	70800000	USD
CY2020	us-gaap	Noninterest Expense NoninterestExpense	491600000	USD
CY2020	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	622500000	USD
CY2020	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	115900000	USD
CY2020	us-gaap	Net Income Loss NetIncomeLoss	506600000	USD
CY2019	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	1040400000	USD
CY2019	us-gaap	Provision For Loan Lease And Other Losses ProvisionForLoanLeaseAndOtherLosses	19300000	USD
CY2019	us-gaap	Interest Income Expense After Provision For Loan Loss InterestIncomeExpenseAfterProvisionForLoanLoss	1021100000	USD
CY2019	us-gaap	Noninterest Income NoninterestIncome	65100000	USD
CY2019	us-gaap	Noninterest Expense NoninterestExpense	482000000.0	USD
CY2019	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	604200000	USD
CY2019	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	105000000.0	USD
CY2019	us-gaap	Net Income Loss NetIncomeLoss	499200000	USD
CY2021	wal	Revenue From Contracts With Customers RevenueFromContractsWithCustomers	37600000	USD
CY2020	wal	Revenue From Contracts With Customers RevenueFromContractsWithCustomers	29900000	USD
CY2019	wal	Revenue From Contracts With Customers RevenueFromContractsWithCustomers	31100000	USD

Files In Submission

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walex41-descriptionofregis.htm	Edgar Link	pending

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$WAL
WESTERN ALLIANCE BANCORPORATION Stock $wal

2021 Q4 Form 10-K Financial Statement

#000121254522000090 Filed on February 25, 2022

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$WAL WESTERN ALLIANCE BANCORPORATION Stock $wal

2021 Q4 Form 10-K Financial Statement

#000121254522000090 Filed on February 25, 2022

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$WAL
WESTERN ALLIANCE BANCORPORATION Stock $wal