Loans (Financial Impact and TDRs by Concession Type) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($) my_loan	Mar. 31, 2019 USD ($) my_loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | my_loan	3,580	3,836
Pre-TDR Recorded Investment	$ 98	$ 147
Post-TDR Recorded Investment	75	149
Principal Forgiveness [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Recorded Investment	6
Rate Reduction [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Recorded Investment	22	24
Other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Recorded Investment	$ 47	$ 125
Total commercial lending
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | my_loan	13	22
Pre-TDR Recorded Investment	$ 62	$ 105
Post-TDR Recorded Investment	43	109
Total commercial lending | Principal Forgiveness [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Recorded Investment	6
Total commercial lending | Other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Recorded Investment	$ 37	$ 109
Total consumer lending
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | my_loan	3,567	3,814
Pre-TDR Recorded Investment	$ 36	$ 42
Post-TDR Recorded Investment	32	40
Total consumer lending | Rate Reduction [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Recorded Investment	22	24
Total consumer lending | Other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Recorded Investment	$ 10	$ 16