ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Nonperforming Loans and Leases by Class (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	$ 1,093		$ 1,383
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	8		33
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	1,101		1,416
Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	163		265
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	1		0
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	164		265
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	113		96
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	1		0
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	114		96
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	50		169
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	0		0
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	50		169
Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	0		0
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	0		0
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	0		0
Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	930		1,118
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	7		33
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	937		1,151
Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	345		382
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	0		0
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	345		382
Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	203		266
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	0		0
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	203		266
Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	257		333
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	0		0
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	257		333
Home equity loans serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	47	[1]	59	[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	47	[1]	59	[1]
Home equity lines of credit serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	25	[1]	30	[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]	30	[1]
Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	21		16
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	0		0
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	21		16
Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	11		3
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	6		31
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	17		34
Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	16		19
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	1		2
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	17		21
Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccruing	5		10
Financing Receivable, Recorded Investment, Accruing and 90 Days or More Delinquent	0		0
Financing Receivable, Recorded Investment, Total Nonperforming Loans and Leases	$ 5		$ 10

[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.