Asset Quality (Financial Impact and TDRs by Concession Type) (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($) my_loan	Jun. 30, 2018 USD ($) my_loan	Jun. 30, 2019 USD ($) my_loan	Jun. 30, 2018 USD ($) my_loan
Financing Receivable, Modifications [Line Items]
Number of Loans | my_loan	3,554	2,904	7,390	5,915
Pre-TDR Recorded Investment	$ 75	$ 55	$ 222	$ 114
Post-TDR Recorded Investment	68	49	217	103
Principal Forgiveness [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment		1		1
Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	25	18	49	49
Other [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	$ 43	$ 30	$ 168	$ 53
Total commercial lending [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | my_loan	15	15	37	47
Pre-TDR Recorded Investment	$ 31	$ 20	$ 136	$ 30
Post-TDR Recorded Investment	28	18	137	26
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	1	1	2
Total commercial lending [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	$ 27	$ 17	$ 136	$ 24
Total consumer lending [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | my_loan	3,539	2,889	7,353	5,868
Pre-TDR Recorded Investment	$ 44	$ 35	$ 86	$ 84
Post-TDR Recorded Investment	40	31	80	77
Total consumer lending [Member] | Principal Forgiveness [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment		1		1
Total consumer lending [Member] | Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	24	17	48	47
Total consumer lending [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	$ 16	$ 13	$ 32	$ 29