Asset Quality (Financial Impact and TDRs by Concession Type) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2016 USD ($) loans	Mar. 31, 2015 USD ($) loans
Financing Receivable, Modifications [Line Items]
Number of Loans | loans	3,007	2,776
Pre-TDR Recorded Investment	$ 236	$ 134
Post-TDR Recorded Investment	216	120
Principal Forgiveness [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment		1
Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	54	44
Other [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	$ 162	$ 75
Total commercial lending [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | loans	42	38
Pre-TDR Recorded Investment	$ 168	$ 63
Post-TDR Recorded Investment	152	53
Total commercial lending [Member] | Principal Forgiveness [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment		1
Total commercial lending [Member] | Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	10	2
Total commercial lending [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	$ 142	$ 50
Total consumer lending [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | loans	2,965	2,738
Pre-TDR Recorded Investment	$ 68	$ 71
Post-TDR Recorded Investment	64	67
Total consumer lending [Member] | Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	44	42
Total consumer lending [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Post-TDR Recorded Investment	$ 20	$ 25