ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Nonperforming Loans and Leases by Class (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccruing		$ 1,051	$ 1,093
Accruing and 90 Days or More Delinquent		9	8
Total Nonperforming Loans and Leases		1,060	1,101
Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccruing		147	163
Accruing and 90 Days or More Delinquent		1	1
Total Nonperforming Loans and Leases		148	164
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccruing		70	113
Accruing and 90 Days or More Delinquent		1	1
Total Nonperforming Loans and Leases		71	114
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccruing		77	50
Accruing and 90 Days or More Delinquent		0	0
Total Nonperforming Loans and Leases		77	50
Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccruing		0	0
Accruing and 90 Days or More Delinquent		0	0
Total Nonperforming Loans and Leases		0	0
Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccruing		904	930
Accruing and 90 Days or More Delinquent		8	7
Total Nonperforming Loans and Leases		912	937
Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccruing		331	345
Accruing and 90 Days or More Delinquent		0	0
Total Nonperforming Loans and Leases		331	345
Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccruing		135	203
Accruing and 90 Days or More Delinquent		0	0
Total Nonperforming Loans and Leases		135	203
Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccruing		272	257
Accruing and 90 Days or More Delinquent		0	0
Total Nonperforming Loans and Leases		272	257
Home equity loans serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccruing	[1]	38	47
Accruing and 90 Days or More Delinquent	[1]	0	0
Total Nonperforming Loans and Leases	[1]	38	47
Home equity lines of credit serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccruing	[1]	32	25
Accruing and 90 Days or More Delinquent	[1]	0	0
Total Nonperforming Loans and Leases	[1]	32	25
Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccruing		42	21
Accruing and 90 Days or More Delinquent		0	0
Total Nonperforming Loans and Leases		42	21
Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccruing		35	11
Accruing and 90 Days or More Delinquent		6	6
Total Nonperforming Loans and Leases		41	17
Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccruing		16	16
Accruing and 90 Days or More Delinquent		0	1
Total Nonperforming Loans and Leases		16	17
Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccruing		3	5
Accruing and 90 Days or More Delinquent		2	0
Total Nonperforming Loans and Leases		$ 5	$ 5

[1] The Company’s SBO portfolio consists of purchased home equity loans and lines that were originally serviced by others. The Company now services a portion of this portfolio internally.