Loans and Related Allowance for Credit Losses (Nonperforming Assets) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Nonperforming loans, without allowance for credit losses	$ 700	$ 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	$ 2,138	2,286
OREO and foreclosed assets	41	51
Total nonperforming assets	$ 2,179	$ 2,337
Nonperforming loans to total loans	0.90%	0.94%
Nonperforming assets to total loans, OREO and foreclosed assets	0.92%	0.97%
Nonperforming assets to total assets	0.46%	0.50%
Total commercial | Nonperforming loans
Nonaccrual loans	$ 749	$ 923
Total consumer | Nonperforming loans
Nonaccrual loans	$ 1,389	$ 1,363