Asset Quality (Financial Impact and TDRs by Concession Type) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($) loans	Mar. 31, 2018 USD ($) loans
Financing Receivable, Modifications [Line Items]
Number of Loans | loans	3,836	3,011
Pre-TDR Recorded Investment	$ 147	$ 59
Post-TDR Recorded Investment	149	54
Principal Forgiveness [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment
Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	24	31
Other [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	$ 125	$ 23
Total commercial lending [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | loans	22	32
Pre-TDR Recorded Investment	$ 105	$ 10
Post-TDR Recorded Investment	109	8
Total commercial lending [Member] | Principal Forgiveness [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment
Total commercial lending [Member] | Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment		1
Total commercial lending [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	$ 109	$ 7
Total consumer lending [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | loans	3,814	2,979
Pre-TDR Recorded Investment	$ 42	$ 49
Post-TDR Recorded Investment	40	46
Total consumer lending [Member] | Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	24	30
Total consumer lending [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	$ 16	$ 16