ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Nonperforming Loans and Leases by Class (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	$ 1,127		$ 1,093
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	9		8
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	1,136		1,101
Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	155		163
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	3		1
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	158		164
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	94		113
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	3		1
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	97		114
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	60		50
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	0		0
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	60		50
Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	1		0
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	0		0
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	1		0
Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	972		930
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	6		7
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	978		937
Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	347		345
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	0		0
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	347		345
Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	210		203
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	0		0
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	210		203
Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	270		257
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	0		0
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	270		257
Home equity loans serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	44	[1]	47	[1]
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	0	[1]	0	[1]
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	44	[1]	47	[1]
Home equity lines of credit serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	25	[1]	25	[1]
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	0	[1]	0	[1]
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	25	[1]	25	[1]
Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	30		21
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	0		0
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	30		21
Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	26		11
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	4		6
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	30		17
Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	16		16
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	0		1
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	16		17
Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	4		5
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	2		0
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	$ 6		$ 5

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