Loans and ACL (Summary of the Primary Reason Loan Modifications Were Classified as TDRs) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Commercial and Industrial [Member]
Summary Of Reason Modifications Were Considered TDRs [Line Items]
TDR rate modification	$ 112	$ 99	$ 51
TDR structure modification	48	27	63
TDR increase to allowance	4	3	0
CRE Income Producing Properties [Member]
Summary Of Reason Modifications Were Considered TDRs [Line Items]
TDR rate modification	18	33	55
TDR structure modification	18	44	29
TDR increase to allowance	0	1	0
CRE Construction And Development [Member]
Summary Of Reason Modifications Were Considered TDRs [Line Items]
TDR rate modification	25	51	56
TDR structure modification	22	20	50
TDR increase to allowance	0	(2)	(2)
Direct Retail Lending [Member]
Summary Of Reason Modifications Were Considered TDRs [Line Items]
TDR rate modification	32	45	120
TDR structure modification	4	9	17
TDR increase to allowance	6	6	35
Retail Revolving Credit [Member]
Summary Of Reason Modifications Were Considered TDRs [Line Items]
TDR rate modification	24	26	30
TDR structure modification	0	0	0
TDR increase to allowance	4	4	5
Retail Residential Mortgage-Nonguaranteed [Member]
Summary Of Reason Modifications Were Considered TDRs [Line Items]
TDR rate modification	127	103	241
TDR structure modification	36	68	88
TDR increase to allowance	16	11	22
Retail Residential Mortgage-Government Guaranteed [Member]
Summary Of Reason Modifications Were Considered TDRs [Line Items]
TDR rate modification	282	141	85
TDR structure modification	0	0	0
TDR increase to allowance	12	12	9
Retail Sales Finance [Member]
Summary Of Reason Modifications Were Considered TDRs [Line Items]
TDR rate modification	1	4	16
TDR structure modification	14	7	0
TDR increase to allowance	3	3	4
Retail Other Lending Subsidiaries [Member]
Summary Of Reason Modifications Were Considered TDRs [Line Items]
TDR rate modification	130	167	123
TDR structure modification	0	0	2
TDR increase to allowance	$ 17	$ 34	$ 35