Loans and ACL - Types of Modifications and Impact to Allowance (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Newly Designated TDRs [Member] | Commercial | Commercial and industrial
Financing Receivable, Modifications [Line Items]
Impact To ALLL	$ 1	$ 1	$ 3	$ 3
Newly Designated TDRs [Member] | Commercial | CRE-income producing properties
Financing Receivable, Modifications [Line Items]
Impact To ALLL	0	0	0	0
Newly Designated TDRs [Member] | Commercial | CRE-construction and development
Financing Receivable, Modifications [Line Items]
Impact To ALLL	0	0	1	0
Newly Designated TDRs [Member] | Retail | Direct retail lending
Financing Receivable, Modifications [Line Items]
Impact To ALLL	0	0	0	0
Newly Designated TDRs [Member] | Retail | Revolving credit
Financing Receivable, Modifications [Line Items]
Impact To ALLL	1	1	3	3
Newly Designated TDRs [Member] | Retail | Residential mortgage-nonguaranteed
Financing Receivable, Modifications [Line Items]
Impact To ALLL	2	2	12	5
Newly Designated TDRs [Member] | Retail | Residential mortgage-government guaranteed
Financing Receivable, Modifications [Line Items]
Impact To ALLL	3	7	9	12
Newly Designated TDRs [Member] | Retail | Sales finance
Financing Receivable, Modifications [Line Items]
Impact To ALLL	0	0	0	0
Newly Designated TDRs [Member] | Retail | Other lending subsidiaries
Financing Receivable, Modifications [Line Items]
Impact To ALLL	8	6	16	16
Newly Designated TDRs [Member] | Rate | Commercial | Commercial and industrial
Financing Receivable, Modifications [Line Items]
TDRs	17	8	72	99
Newly Designated TDRs [Member] | Rate | Commercial | CRE-income producing properties
Financing Receivable, Modifications [Line Items]
TDRs	0	0	6	4
Newly Designated TDRs [Member] | Rate | Commercial | CRE-construction and development
Financing Receivable, Modifications [Line Items]
TDRs	0	0	8	1
Newly Designated TDRs [Member] | Rate | Retail | Direct retail lending
Financing Receivable, Modifications [Line Items]
TDRs	2	5	7	10
Newly Designated TDRs [Member] | Rate | Retail | Revolving credit
Financing Receivable, Modifications [Line Items]
TDRs	5	4	14	13
Newly Designated TDRs [Member] | Rate | Retail | Residential mortgage-nonguaranteed
Financing Receivable, Modifications [Line Items]
TDRs	25	30	119	65
Newly Designated TDRs [Member] | Rate | Retail | Residential mortgage-government guaranteed
Financing Receivable, Modifications [Line Items]
TDRs	54	118	170	217
Newly Designated TDRs [Member] | Rate | Retail | Sales finance
Financing Receivable, Modifications [Line Items]
TDRs	0	0	0	0
Newly Designated TDRs [Member] | Rate | Retail | Other lending subsidiaries
Financing Receivable, Modifications [Line Items]
TDRs	62	44	140	118
Newly Designated TDRs [Member] | Structure | Commercial | Commercial and industrial
Financing Receivable, Modifications [Line Items]
TDRs	36	23	92	39
Newly Designated TDRs [Member] | Structure | Commercial | CRE-income producing properties
Financing Receivable, Modifications [Line Items]
TDRs	4	1	8	8
Newly Designated TDRs [Member] | Structure | Commercial | CRE-construction and development
Financing Receivable, Modifications [Line Items]
TDRs	1	3	2	4
Newly Designated TDRs [Member] | Structure | Retail | Direct retail lending
Financing Receivable, Modifications [Line Items]
TDRs	1	0	3	1
Newly Designated TDRs [Member] | Structure | Retail | Revolving credit
Financing Receivable, Modifications [Line Items]
TDRs	0	0	0	0
Newly Designated TDRs [Member] | Structure | Retail | Residential mortgage-nonguaranteed
Financing Receivable, Modifications [Line Items]
TDRs	17	22	29	36
Newly Designated TDRs [Member] | Structure | Retail | Residential mortgage-government guaranteed
Financing Receivable, Modifications [Line Items]
TDRs	0	0	0	0
Newly Designated TDRs [Member] | Structure | Retail | Sales finance
Financing Receivable, Modifications [Line Items]
TDRs	1	2	5	5
Newly Designated TDRs [Member] | Structure | Retail | Other lending subsidiaries
Financing Receivable, Modifications [Line Items]
TDRs	0	0	0	0
Re-Modification of Previously Designated TDRs [Member]
Financing Receivable, Modifications [Line Items]
Impact To ALLL	0	0	0	0
Re-Modification of Previously Designated TDRs [Member] | Rate
Financing Receivable, Modifications [Line Items]
TDRs	63	19	148	48
Re-Modification of Previously Designated TDRs [Member] | Structure
Financing Receivable, Modifications [Line Items]
TDRs	$ 4	$ 16	$ 26	$ 26