ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Nonperforming Loans and Leases by Class (Details) - USD ($) $ in Millions		Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans		$ 932	$ 1,045
Loans accruing and 90 days or more past due		30	26
GNMA
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans sold with right to repurchase		28	32
Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans accruing and 90 days or more past due		15	18
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans		325	387
Loans accruing and 90 days or more past due		7	2
Commercial | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans		297	322
Loans accruing and 90 days or more past due		5	2
Commercial | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans		28	50
Loans accruing and 90 days or more past due		2	0
Commercial | Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans		0	15
Loans accruing and 90 days or more past due		0	0
Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans		607	658
Loans accruing and 90 days or more past due		23	24
Retail | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans	[1]	124	144
Loans accruing and 90 days or more past due	[1]	15	18
Retail | Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans		76	98
Loans accruing and 90 days or more past due		0	0
Retail | Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans		236	243
Loans accruing and 90 days or more past due		0	0
Retail | Home equity loans serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans		26	32
Loans accruing and 90 days or more past due		0	0
Retail | Home equity lines of credit serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans		21	33
Loans accruing and 90 days or more past due		0	0
Retail | Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans		66	50
Loans accruing and 90 days or more past due		0	0
Retail | Education
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans		38	38
Loans accruing and 90 days or more past due		3	5
Retail | Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans		15	16
Loans accruing and 90 days or more past due		0	0
Retail | Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans		5	4
Loans accruing and 90 days or more past due		$ 5	$ 1

[1] Nonperforming balances exclude first lien residential mortgage loans that are 100% guaranteed by the Federal Housing Administration. These loans, which are accruing and 90 days or more past due, totaled $15 million and $18 million as of September 30, 2017 and December 31, 2016, respectively. Nonperforming balances also exclude guaranteed residential mortgage loans sold to GNMA for which the Company has the right, but not the obligation, to repurchase. These loans totaled $28 million and $32 million as of September 30, 2017 and December 31, 2016, respectively. These loans are consolidated on the Company’s Consolidated Balance Sheets.