Loans and ACL (Summary of the Pre-Default Balance for Modifications That Experienced a Payment Default) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Commercial and Industrial [Member]
Financing Receivable, Modifications [Line Items]
Modifications that defaulted during the period that had been classified as a TDR during the previous 12 months	$ 5	$ 5	$ 8
CRE Income Producing Properties [Member]
Financing Receivable, Modifications [Line Items]
Modifications that defaulted during the period that had been classified as a TDR during the previous 12 months	1	11	6
CRE Construction And Development [Member]
Financing Receivable, Modifications [Line Items]
Modifications that defaulted during the period that had been classified as a TDR during the previous 12 months	4	4	14
Direct Retail Lending [Member]
Financing Receivable, Modifications [Line Items]
Modifications that defaulted during the period that had been classified as a TDR during the previous 12 months	2	4	8
Retail Revolving Credit [Member]
Financing Receivable, Modifications [Line Items]
Modifications that defaulted during the period that had been classified as a TDR during the previous 12 months	9	10	12
Retail Residential Mortgage-Nonguaranteed [Member]
Financing Receivable, Modifications [Line Items]
Modifications that defaulted during the period that had been classified as a TDR during the previous 12 months	23	17	36
Retail Sales Finance [Member]
Financing Receivable, Modifications [Line Items]
Modifications that defaulted during the period that had been classified as a TDR during the previous 12 months	1	1	0
Retail Other Lending Subsidiaries [Member]
Financing Receivable, Modifications [Line Items]
Modifications that defaulted during the period that had been classified as a TDR during the previous 12 months	$ 33	$ 26	$ 12