ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Recorded Investment in Retail Loans by Delinquency Status (Details) (Loans and Leases, USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
Investment in loan balance	$ 94,494		$ 93,410
Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Investment in loan balance	50,512		50,184
Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	11,373		11,352
1-29 Days Past Due	80		114
30-89 Days Past Due	97		97
90 Days or More Past Due	258		269
Investment in loan balance	11,808		11,832
Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	2,817		2,997
1-29 Days Past Due	193		222
30-89 Days Past Due	57		60
90 Days or More Past Due	145		145
Investment in loan balance	3,212		3,424
Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	14,471		14,705
1-29 Days Past Due	386		447
30-89 Days Past Due	77		73
90 Days or More Past Due	193		198
Investment in loan balance	15,127		15,423
Home equity loans serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,082	[1]	1,101	[1]
1-29 Days Past Due	67	[1]	78	[1]
30-89 Days Past Due	22	[1]	26	[1]
90 Days or More Past Due	21	[1]	23	[1]
Investment in loan balance	1,192	[1]	1,228	[1]
Home equity lines of credit serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	455	[1]	455	[1]
1-29 Days Past Due	59	[1]	66	[1]
30-89 Days Past Due	11	[1]	10	[1]
90 Days or More Past Due	19	[1]	19	[1]
Investment in loan balance	544	[1]	550	[1]
Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	12,378		11,839
1-29 Days Past Due	695		758
30-89 Days Past Due	85		93
90 Days or More Past Due	21		16
Investment in loan balance	13,179		12,706
Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	2,725		2,106
1-29 Days Past Due	70		108
30-89 Days Past Due	27		25
90 Days or More Past Due	30		17
Investment in loan balance	2,852		2,256
Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,517		1,615
1-29 Days Past Due	37		39
30-89 Days Past Due	18		22
90 Days or More Past Due	16		17
Investment in loan balance	1,588		1,693
Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	929		985
1-29 Days Past Due	61		65
30-89 Days Past Due	15		18
90 Days or More Past Due	5		4
Investment in loan balance	1,010		1,072
Total retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	47,747		47,155
1-29 Days Past Due	1,648		1,897
30-89 Days Past Due	409		424
90 Days or More Past Due	708		708
Investment in loan balance	$ 50,512		$ 50,184

[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.