Asset Quality (Financial Impact and TDRs by Concession Type) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) loans	Dec. 31, 2017 USD ($) loans	Dec. 31, 2016 USD ($) loans
Financing Receivable, Modifications [Line Items]
Number of Loans | loans	12,181	12,113	11,405
Pre-TDR Recorded Investment	$ 435	$ 541	$ 769
Post-TDR Recorded Investment	398	495	703
Principal Forgiveness
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	3	18
Rate Reduction
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	153	153	214
Other
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	$ 242	$ 324	$ 489
Total commercial lending
Financing Receivable, Modifications [Line Items]
Number of Loans | loans	85	120	143
Pre-TDR Recorded Investment	$ 272	$ 293	$ 524
Post-TDR Recorded Investment	248	252	470
Total commercial lending | Principal Forgiveness
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	2	18
Total commercial lending | Rate Reduction
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	67	7	57
Total commercial lending | Other
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	$ 179	$ 227	$ 413
Total consumer lending
Financing Receivable, Modifications [Line Items]
Number of Loans | loans	12,096	11,993	11,262
Pre-TDR Recorded Investment	$ 163	$ 248	$ 245
Post-TDR Recorded Investment	150	243	233
Total consumer lending | Principal Forgiveness
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	1
Total consumer lending | Rate Reduction
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	86	146	157
Total consumer lending | Other
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	$ 63	$ 97	$ 76