Loans - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Financing Receivable, Allowance for Credit Loss [Line Items]
Accrued interest receivable	$ 1,200		$ 1,200		$ 1,200
TDRs	1,700		1,700		2,100
Commitments to lend on loans modified in TDRs	164		164		173
Federal Home Loan banks
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans Pledged as Collateral	10,900		10,900		14,100
Line of Credit Facility, Remaining Borrowing Capacity	18,800		18,800		19,600
Federal Reserve Discount Window
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans Pledged as Collateral	26,600		26,600		25,500
Line of Credit Facility, Remaining Borrowing Capacity	19,900		19,900		20,000
Credit Card and Consumer Banking | Performing
Financing Receivable, Allowance for Credit Loss [Line Items]
TDRs	1,100		1,100		1,300
Commercial Banking | Performing
Financing Receivable, Allowance for Credit Loss [Line Items]
TDRs	231		231		$ 442
Domestic credit card: | Domestic Credit Card and Commercial Banking Portfolios [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Revolving loans converted to term during period	$ 37	$ 250	$ 172	$ 499