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, 2020 USD ($) my_loan	Jun. 30, 2019 USD ($) my_loan	Jun. 30, 2020 USD ($) my_loan	Jun. 30, 2019 USD ($) my_loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | my_loan	3,618	3,554	7,198	7,390
Pre-TDR Amortized Cost Basis	$ 204		$ 302
Post-TDR Recorded Investment	212	$ 68	287	$ 217
Pre-TDR Recorded Investment		75		222
Principal Forgiveness [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Recorded Investment	33		39
Rate Reduction [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Recorded Investment	19	25	41	49
Other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Recorded Investment	$ 160	$ 43	$ 207	$ 168
Total commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | my_loan	29	15	42	37
Pre-TDR Amortized Cost Basis	$ 147		$ 209
Post-TDR Recorded Investment	158	$ 28	201	$ 137
Pre-TDR Recorded Investment		31		136
Total commercial | Principal Forgiveness [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Recorded Investment	33		39
Total commercial | Rate Reduction [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Recorded Investment		1		1
Total commercial | Other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Recorded Investment	$ 125	$ 27	$ 162	$ 136
Total consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | my_loan	3,589	3,539	7,156	7,353
Pre-TDR Amortized Cost Basis	$ 57		$ 93
Post-TDR Recorded Investment	54	$ 40	86	$ 80
Pre-TDR Recorded Investment		44		86
Total consumer | Principal Forgiveness [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Recorded Investment
Total consumer | Rate Reduction [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Recorded Investment	19	24	41	48
Total consumer | Other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Post-TDR Recorded Investment	$ 35	$ 16	$ 45	$ 32