Asset Quality (Financial Impact and TDRs by Concession Type) (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) loans	Sep. 30, 2017 USD ($) loans	Sep. 30, 2018 USD ($) loans	Sep. 30, 2017 USD ($) loans
Financing Receivable, Modifications [Line Items]
Number of Loans | loans	3,165	2,990	9,080	8,946
Pre-TDR Recorded Investment	$ 160	$ 96	$ 274	$ 435
Post-TDR Recorded Investment	149	95	252	393
Principal Forgiveness [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	2	14	3	18
Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	43	36	92	122
Other [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	$ 104	$ 45	$ 157	$ 253
Total commercial lending [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | loans	18	25	65	107
Pre-TDR Recorded Investment	$ 115	$ 44	$ 145	$ 256
Post-TDR Recorded Investment	107	44	133	215
Total commercial lending [Member] | Principal Forgiveness [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	2	14	2	18
Total commercial lending [Member] | Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	24		26	6
Total commercial lending [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	$ 81	$ 30	$ 105	$ 191
Total consumer lending [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | loans	3,147	2,965	9,015	8,839
Pre-TDR Recorded Investment	$ 45	$ 52	$ 129	$ 179
Post-TDR Recorded Investment	42	51	119	178
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	19	36	66	116
Total consumer lending [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	$ 23	$ 15	$ 52	$ 62