Asset Quality - Additional Information (Details) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2022 USD ($) loan	Mar. 31, 2021 USD ($) loan	Dec. 31, 2021 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of carrying amount of our commercial nonperforming loans outstanding	62.00%
Percentage of nonperforming loans outstanding face value	73.00%
Percentage of loans held for sale and other nonperforming assets	81.00%
Net reduction to interest income	$ 5	$ 7
Commitments outstanding to lend additional funds to borrowers (less than $1 million)	1		$ 15
Financial receivable, modifications, subsequent default, recorded investment	$ 8	$ 1
Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDRs, period for default	90 days
Number of loans | loan	4	2
Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDRs, period for default	60 days
Number of loans | loan	38	36
Continuing operations | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Decrease in ALLL	$ 29
Decrease in ALLL (as a percent)	4.20%
Continuing operations | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Decrease in ALLL	$ 15
Decrease in ALLL (as a percent)	4.00%
PPP
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income (residential)	$ 886
Nonperforming financial instruments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonperforming loans on nonaccrual status with no allowance	301
Real estate — residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivable, modifications, subsequent default, recorded investment	$ 126		$ 104