ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Nonperforming Loans and Leases by Class (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans		$ 797	$ 871
Loans accruing and 90 days or more past due		25	32
GNMA loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans sold with right to repurchase		133	30
Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans accruing and 90 days or more past due		12	15
Commercial | Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans		201	265
Loans accruing and 90 days or more past due		1	8
Commercial | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans		194	238
Loans accruing and 90 days or more past due		1	5
Commercial | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans		7	27
Loans accruing and 90 days or more past due		0	3
Commercial | Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans		0	0
Loans accruing and 90 days or more past due		0	0
Retail | Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans		596	606
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]	136	128
Loans accruing and 90 days or more past due	[1]	15	16
Retail | Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans		50	72
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		231	233
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		17	25
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		15	18
Loans accruing and 90 days or more past due		0	0
Retail | Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans		81	70
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		2	3
Retail | Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans		20	17
Loans accruing and 90 days or more past due		0	0
Retail | Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans		8	5
Loans accruing and 90 days or more past due		$ 7	$ 5

[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 $12 million and $15 million as of December 31, 2018 and 2017, 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 $133 million and $30 million as of December 31, 2018 and 2017, respectively. These loans are included in the Company’s Consolidated Balance Sheets.