Loans and ACL (Summary of the Primary Reason Loan Modifications Were Classified as TDRs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Commercial and Industrial [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
ALLL impact	$ 2	$ 4	$ 3
CRE-Income Producing Properties [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
ALLL impact	0	0	1
CRE-Construction And Development [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
ALLL impact	1	0	(2)
Direct Retail Lending [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
ALLL impact	4	6	6
Retail Revolving Credit [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
ALLL impact	4	4	4
Retail Residential Mortgage-Nonguaranteed [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
ALLL impact	9	16	11
Retail Residential Mortgage-Government Guaranteed [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
ALLL impact	7	12	12
Retail Sales Finance [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
ALLL impact	1	3	3
Retail Other Lending Subsidiaries [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
ALLL impact	17	17	34
Types of Modifications - Rate | Commercial and Industrial [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
TDRs	99	112	99
Types of Modifications - Rate | CRE-Income Producing Properties [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
TDRs	9	18	33
Types of Modifications - Rate | CRE-Construction And Development [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
TDRs	8	25	51
Types of Modifications - Rate | Direct Retail Lending [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
TDRs	16	32	45
Types of Modifications - Rate | Retail Revolving Credit [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
TDRs	16	24	26
Types of Modifications - Rate | Retail Residential Mortgage-Nonguaranteed [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
TDRs	88	127	103
Types of Modifications - Rate | Retail Residential Mortgage-Government Guaranteed [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
TDRs	189	282	141
Types of Modifications - Rate | Retail Sales Finance [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
TDRs	0	1	4
Types of Modifications - Rate | Retail Other Lending Subsidiaries [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
TDRs	129	130	167
Types of Modifications - Structure | Commercial and Industrial [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
TDRs	45	48	27
Types of Modifications - Structure | CRE-Income Producing Properties [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
TDRs	15	18	44
Types of Modifications - Structure | CRE-Construction And Development [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
TDRs	25	22	20
Types of Modifications - Structure | Direct Retail Lending [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
TDRs	4	4	9
Types of Modifications - Structure | Retail Revolving Credit [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
TDRs	0	0	0
Types of Modifications - Structure | Retail Residential Mortgage-Nonguaranteed [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
TDRs	37	36	68
Types of Modifications - Structure | Retail Residential Mortgage-Government Guaranteed [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
TDRs	0	0	0
Types of Modifications - Structure | Retail Sales Finance [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
TDRs	10	14	7
Types of Modifications - Structure | Retail Other Lending Subsidiaries [Member]
Summary Of Reason Loan Modifications Were Considered TDRs [Line Items]
TDRs	$ 0	$ 0	$ 0