ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Accruing and Nonaccruing Past Due Amounts (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Financing Receivables, 30 to 89 Days Past Due	$ 510		$ 554
Impaired Financing Receivables, 90 Days or More Past Due	872		1,057
Impaired Financing Receivables, Total Past Due	1,382		1,611
Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Financing Receivables, 30 to 89 Days Past Due	86		119
Impaired Financing Receivables, 90 Days or More Past Due	164		265
Impaired Financing Receivables, Total Past Due	250		384
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Financing Receivables, 30 to 89 Days Past Due	57		61
Impaired Financing Receivables, 90 Days or More Past Due	114		96
Impaired Financing Receivables, Total Past Due	171		157
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Financing Receivables, 30 to 89 Days Past Due	26		34
Impaired Financing Receivables, 90 Days or More Past Due	50		169
Impaired Financing Receivables, Total Past Due	76		203
Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Financing Receivables, 30 to 89 Days Past Due	3		24
Impaired Financing Receivables, 90 Days or More Past Due	0		0
Impaired Financing Receivables, Total Past Due	3		24
Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Financing Receivables, 30 to 89 Days Past Due	424		435
Impaired Financing Receivables, 90 Days or More Past Due	708		792
Impaired Financing Receivables, Total Past Due	1,132		1,227
Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Financing Receivables, 30 to 89 Days Past Due	97		115
Impaired Financing Receivables, 90 Days or More Past Due	269		261
Impaired Financing Receivables, Total Past Due	366		376
Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Financing Receivables, 30 to 89 Days Past Due	60		68
Impaired Financing Receivables, 90 Days or More Past Due	145		168
Impaired Financing Receivables, Total Past Due	205		236
Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Financing Receivables, 30 to 89 Days Past Due	73		76
Impaired Financing Receivables, 90 Days or More Past Due	198		233
Impaired Financing Receivables, Total Past Due	271		309
Home equity loans serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Financing Receivables, 30 to 89 Days Past Due	26	[1]	32	[1]
Impaired Financing Receivables, 90 Days or More Past Due	23	[1]	36	[1]
Impaired Financing Receivables, Total Past Due	49	[1]	68	[1]
Home equity lines of credit serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Financing Receivables, 30 to 89 Days Past Due	10	[1]	11	[1]
Impaired Financing Receivables, 90 Days or More Past Due	19	[1]	24	[1]
Impaired Financing Receivables, Total Past Due	29	[1]	35	[1]
Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Financing Receivables, 30 to 89 Days Past Due	93		44
Impaired Financing Receivables, 90 Days or More Past Due	16		9
Impaired Financing Receivables, Total Past Due	109		53
Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Financing Receivables, 30 to 89 Days Past Due	25		45
Impaired Financing Receivables, 90 Days or More Past Due	17		33
Impaired Financing Receivables, Total Past Due	42		78
Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Financing Receivables, 30 to 89 Days Past Due	22		22
Impaired Financing Receivables, 90 Days or More Past Due	17		21
Impaired Financing Receivables, Total Past Due	39		43
Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Financing Receivables, 30 to 89 Days Past Due	18		22
Impaired Financing Receivables, 90 Days or More Past Due	4		7
Impaired Financing Receivables, Total Past Due	$ 22		$ 29

[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.