Loans and ACL - Types of Modifications and Impact to Allowance (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Commercial and industrial
Summary Of Reason Modifications Were Considered TDRs [Line Items]
Types of Modifications, Rate	$ 10	$ 19	$ 105	$ 68
Types of Modifications, Structure	34	11	57	35
Impact To ALLL	1	0	3	2
CRE-income producing properties
Summary Of Reason Modifications Were Considered TDRs [Line Items]
Types of Modifications, Rate	4	0	15	4
Types of Modifications, Structure	4	1	12	14
Impact To ALLL	0	0	0	0
CRE-construction and development
Summary Of Reason Modifications Were Considered TDRs [Line Items]
Types of Modifications, Rate	2	5	6	5
Types of Modifications, Structure	4	9	7	21
Impact To ALLL	0	0	0	0
Direct retail lending
Summary Of Reason Modifications Were Considered TDRs [Line Items]
Types of Modifications, Rate	5	6	13	12
Types of Modifications, Structure	0	3	1	3
Impact To ALLL	0	1	0	3
Revolving credit
Summary Of Reason Modifications Were Considered TDRs [Line Items]
Types of Modifications, Rate	4	4	13	12
Types of Modifications, Structure	0	0	0	0
Impact To ALLL	1	1	3	3
Residential mortgage-nonguaranteed
Summary Of Reason Modifications Were Considered TDRs [Line Items]
Types of Modifications, Rate	12	21	50	65
Types of Modifications, Structure	35	7	49	29
Impact To ALLL	2	2	5	7
Residential mortgage-government guaranteed
Summary Of Reason Modifications Were Considered TDRs [Line Items]
Types of Modifications, Rate	105	42	213	151
Types of Modifications, Structure	0	0	0	0
Impact To ALLL	7	2	12	6
Sales finance
Summary Of Reason Modifications Were Considered TDRs [Line Items]
Types of Modifications, Rate	0	0	0	0
Types of Modifications, Structure	2	3	5	8
Impact To ALLL	0	1	0	1
Retail other lending subsidiaries
Summary Of Reason Modifications Were Considered TDRs [Line Items]
Types of Modifications, Rate	44	32	118	92
Types of Modifications, Structure	0	0	0	0
Impact To ALLL	$ 6	$ 5	$ 16	$ 13