Loans and Related Allowance for Credit Losses (Financial Impact and TDRs by Concession Type) (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($) loan	Jun. 30, 2020 USD ($) loan	Jun. 30, 2021 USD ($) loan	Jun. 30, 2020 USD ($) loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	1,397	3,618	3,512	7,198
Pre-TDR Amortized Cost Basis	$ 127	$ 204	$ 252	$ 302
Post-TDR Amortized Cost Basis	103	212	225	287
Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Amortized Cost Basis	12	19	28	41
Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Amortized Cost Basis	$ 91	160	$ 197	207
Principal Forgiveness
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Amortized Cost Basis		$ 33		$ 39
Total commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	11	29	30	42
Pre-TDR Amortized Cost Basis	$ 104	$ 147	$ 197	$ 209
Post-TDR Amortized Cost Basis	82	158	176	201
Total commercial | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Amortized Cost Basis	$ 82	125	$ 176	162
Total commercial | Principal Forgiveness
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Amortized Cost Basis		$ 33		$ 39
Total consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	1,386	3,589	3,482	7,156
Pre-TDR Amortized Cost Basis	$ 23	$ 57	$ 55	$ 93
Post-TDR Amortized Cost Basis	21	54	49	86
Total consumer | Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Amortized Cost Basis	12	19	28	41
Total consumer | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Amortized Cost Basis	$ 9	$ 35	$ 21	$ 45