Loans - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Financing Receivable, Allowance for Credit Loss [Line Items]
Accrued interest receivable	$ 1,100		$ 1,200
TDRs	2,000		2,100
Commitments to lend on loans modified in TDRs	178		173
Federal Home Loan banks
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans Pledged as Collateral	12,800		14,100
Line of Credit Facility, Remaining Borrowing Capacity	18,400		19,600
Federal Reserve Discount Window
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans Pledged as Collateral	28,800		25,500
Line of Credit Facility, Remaining Borrowing Capacity	22,900		20,000
Credit Card and Consumer Banking | Performing
Financing Receivable, Allowance for Credit Loss [Line Items]
TDRs	1,300		1,300
Commercial Banking | Performing
Financing Receivable, Allowance for Credit Loss [Line Items]
TDRs	354		$ 442
Domestic credit card: | Credit Card
Financing Receivable, Allowance for Credit Loss [Line Items]
Revolving loans converted to term during period	$ 97	$ 160