Asset Quality (Financial Impact and TDRs by Concession Type) (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($) my_loan	Sep. 30, 2018 USD ($) my_loan	Sep. 30, 2019 USD ($) my_loan	Sep. 30, 2018 USD ($) my_loan
Financing Receivable, Modifications [Line Items]
Number of Loans | my_loan	3,677	3,165	11,067	9,080
Pre-TDR Recorded Investment	$ 142	$ 160	$ 364	$ 274
Post-TDR Recorded Investment	115	149	332	252
Principal Forgiveness [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment		2		3
Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	24	43	73	92
Other [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	$ 91	$ 104	$ 259	$ 157
Total commercial lending [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | my_loan	21	18	58	65
Pre-TDR Recorded Investment	$ 97	$ 115	$ 233	$ 145
Post-TDR Recorded Investment	72	107	209	133
Total commercial lending [Member] | Principal Forgiveness [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment		2		2
Total commercial lending [Member] | Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment		24	1	26
Total commercial lending [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	$ 72	$ 81	$ 208	$ 105
Total consumer lending [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | my_loan	3,656	3,147	11,009	9,015
Pre-TDR Recorded Investment	$ 45	$ 45	$ 131	$ 129
Post-TDR Recorded Investment	43	42	123	119
Total consumer lending [Member] | Principal Forgiveness [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment				1
Total consumer lending [Member] | Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	24	19	72	66
Total consumer lending [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	$ 19	$ 23	$ 51	$ 52