Loans and Related Allowance for Credit Losses (Financial Impact and TDRs by Concession Type) (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) my_loan	Sep. 30, 2019 USD ($) my_loan	Sep. 30, 2020 USD ($) my_loan	Sep. 30, 2019 USD ($) my_loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | my_loan	2,785	3,677	9,983	11,067
Pre-TDR Amortized Cost Basis	$ 141		$ 443
Post-TDR Amortized Cost Basis	119		406
Pre-TDR Recorded Investment		$ 142		$ 364
Post-TDR Recorded Investment		115		332
Principal Forgiveness [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Amortized Cost Basis			39
Post-TDR Recorded Investment
Rate Reduction [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Amortized Cost Basis	36		77
Post-TDR Recorded Investment		24		73
Other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Amortized Cost Basis	$ 83		$ 290
Post-TDR Recorded Investment		$ 91		$ 259
Total commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | my_loan	16	21	58	58
Pre-TDR Amortized Cost Basis	$ 95		$ 304
Post-TDR Amortized Cost Basis	79		280
Pre-TDR Recorded Investment		$ 97		$ 233
Post-TDR Recorded Investment		72		209
Total commercial | Principal Forgiveness [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Amortized Cost Basis			39
Post-TDR Recorded Investment
Total commercial | Rate Reduction [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Amortized Cost Basis	10		10
Post-TDR Recorded Investment				1
Total commercial | Other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Amortized Cost Basis	$ 69		$ 231
Post-TDR Recorded Investment		$ 72		$ 208
Total consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | my_loan	2,769	3,656	9,925	11,009
Pre-TDR Amortized Cost Basis	$ 46		$ 139
Post-TDR Amortized Cost Basis	40		126
Pre-TDR Recorded Investment		$ 45		$ 131
Post-TDR Recorded Investment		43		123
Total consumer | Principal Forgiveness [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Amortized Cost Basis
Post-TDR Recorded Investment
Total consumer | Rate Reduction [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Amortized Cost Basis	26		67
Post-TDR Recorded Investment		24		72
Total consumer | Other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Amortized Cost Basis	$ 14		$ 59
Post-TDR Recorded Investment		$ 19		$ 51