Loans - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Financing Receivable, Allowance for Credit Loss [Line Items]
Accrued interest receivable	$ 1,200		$ 1,200		$ 1,200
TDRs	1,800		1,800		2,100
Commitments to lend on loans modified in TDRs	173		173		173
Federal Home Loan banks
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans Pledged as Collateral	11,600		11,600		14,100
Line of Credit Facility, Remaining Borrowing Capacity	19,200		19,200		19,600
Federal Reserve Discount Window
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans Pledged as Collateral	26,900		26,900		25,500
Line of Credit Facility, Remaining Borrowing Capacity	21,300		21,300		20,000
Credit Card and Consumer Banking | Performing
Financing Receivable, Allowance for Credit Loss [Line Items]
TDRs	1,200		1,200		1,300
Commercial Banking | Performing
Financing Receivable, Allowance for Credit Loss [Line Items]
TDRs	243		243		$ 442
Domestic credit card: | Credit Card
Financing Receivable, Allowance for Credit Loss [Line Items]
Revolving loans converted to term during period	$ 38	$ 89	$ 135	$ 249