ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Nonperforming Loans and Leases by Class (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans	[1]	$ 871	$ 1,045
Loans accruing and 90 days or more past due		32	26
GNMA loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans sold with right to repurchase		30	32
Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans accruing and 90 days or more past due		15	18
Commercial | Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans	[1]	265	387
Loans accruing and 90 days or more past due		8	2
Commercial | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans	[1]	238	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	[1]	27	50
Loans accruing and 90 days or more past due		3	0
Commercial | Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans	[1]	0	15
Loans accruing and 90 days or more past due		0	0
Retail | Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans	[1]	606	658
Loans accruing and 90 days or more past due		24	24
Retail | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans	[1]	128	144
Loans accruing and 90 days or more past due		16	18
Retail | Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans	[1]	72	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	[1]	233	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	[1]	25	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	[1]	18	33
Loans accruing and 90 days or more past due		0	0
Retail | Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans	[1]	70	50
Loans accruing and 90 days or more past due		0	0
Retail | Education
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans	[1]	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	[1]	17	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	[1]	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 December 31, 2017 and 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 $30 million and $32 million as of December 31, 2017 and 2016, respectively. These loans are included in the Company’s Consolidated Balance Sheets.