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Asset Quality - Additional Information (Details) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2021 USD ($) SecurityLoan	Mar. 31, 2020 USD ($) SecurityLoan	Dec. 31, 2020 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income (residential)	$ 100,926		$ 101,185
Loan modifications and forbearance, CARES Act	328
Loans that have received payment deferral or forbearance, CARES Act	384
Accrued interest	$ 242		241
Percentage of carrying amount of our commercial nonperforming loans outstanding	68.00%
Percentage of nonperforming loans outstanding face value	75.00%
Percentage of loans held for sale and other nonperforming assets	81.00%
Net reduction to interest income	$ 7	$ 6
Commitments outstanding to lend additional funds to borrowers (less than $1 million)	14		1
Financial receivable, modifications, subsequent default, recorded investment	1	$ 2
Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income (residential)	71,414		71,980
Accrued interest	$ 143		140
TDRs, period for default	90 days
Number of loans | SecurityLoan	2	0
Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income (residential)	$ 29,512		29,205
Accrued interest	$ 98		101
TDRs, period for default	60 days
Number of loans | SecurityLoan	36	84
Continuing operations | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase in ALLL	$ (162)
Increase in ALLL, percent	(14.70%)
Continuing operations | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase in ALLL	$ (26)
Increase in ALLL, percent	(4.90%)
PPP
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income (residential)	$ 6,500
Real estate — residential mortgage | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income (residential)	10,300		9,298
Nonperforming financial instruments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonperforming loans on nonaccrual status with no allowance	461
Real estate — residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivable, modifications, subsequent default, recorded investment	$ 83		$ 92

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