Loans and Related Allowance for Credit Losses (Nonperforming Assets) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Nonperforming loans, without allowance for credit losses	$ 1,000	$ 800
Minimum
Threshold period of financing receivable past due, writeoff	120 days
Maximum
Threshold period of financing receivable past due, writeoff	180 days
Nonperforming loans
Nonaccrual loans	$ 2,779	2,286
OREO and foreclosed assets	39	51
Total nonperforming assets	$ 2,818	$ 2,337
Nonperforming loans to total loans	0.94%	0.94%
Nonperforming assets to total loans, OREO and foreclosed assets	0.96%	0.97%
Nonperforming assets to total assets	0.51%	0.50%
Total commercial | Nonperforming loans
Nonaccrual loans	$ 1,446	$ 923
Total consumer | Nonperforming loans
Nonaccrual loans	$ 1,333	$ 1,363