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		Jun. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		$ 1,357	$ 1,356
Total		103,551	99,042
Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current		13,571	12,905
Past Due		195	316
Total		13,855	13,318
Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current		1,937	2,245
Past Due		107	148
Total		2,177	2,557
Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current		13,755	13,982
Past Due		275	285
Total		14,418	14,674
Home equity loans serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	781	886
Past Due	[1]	31	40
Total	[1]	860	986
Home equity lines of credit serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	184	296
Past Due	[1]	52	45
Total	[1]	273	389
Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current		12,959	12,670
Past Due		190	194
Total		14,075	13,828
Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current		5,340	4,175
Past Due		71	71
Total		5,516	4,359
Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current		1,539	1,554
Past Due		32	36
Total		1,613	1,634
Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current		1,149	1,013
Past Due		14	17
Total		1,207	1,083
Total retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current		51,215	49,726
Total		53,994	52,828
Financing Receivables, 1 to 29 Days Past Due | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		89	97
Financing Receivables, 1 to 29 Days Past Due | Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		133	164
Financing Receivables, 1 to 29 Days Past Due | Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		388	407
Financing Receivables, 1 to 29 Days Past Due | Home equity loans serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	[1]	48	60
Financing Receivables, 1 to 29 Days Past Due | Home equity lines of credit serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	[1]	37	48
Financing Receivables, 1 to 29 Days Past Due | Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		926	964
Financing Receivables, 1 to 29 Days Past Due | Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		105	113
Financing Receivables, 1 to 29 Days Past Due | Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		42	44
Financing Receivables, 1 to 29 Days Past Due | Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		44	53
Financing Receivables, 1 to 29 Days Past Due | Total retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		1,812	1,950
Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		293	383
Financing Receivables, 30 to 59 Days Past Due | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		40	54
Financing Receivables, 30 to 59 Days Past Due | Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		20	32
Financing Receivables, 30 to 59 Days Past Due | Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		44	60
Financing Receivables, 30 to 59 Days Past Due | Home equity loans serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	[1]	10	14
Financing Receivables, 30 to 59 Days Past Due | Home equity lines of credit serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	[1]	12	10
Financing Receivables, 30 to 59 Days Past Due | Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		122	127
Financing Receivables, 30 to 59 Days Past Due | Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		18	19
Financing Receivables, 30 to 59 Days Past Due | Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		10	11
Financing Receivables, 30 to 59 Days Past Due | Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		6	8
Financing Receivables, 30 to 59 Days Past Due | Total retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		282	335
Financing Receivables 60 To 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		133	124
Financing Receivables 60 To 89 Days Past Due | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		10	16
Financing Receivables 60 To 89 Days Past Due | Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		8	12
Financing Receivables 60 To 89 Days Past Due | Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		24	20
Financing Receivables 60 To 89 Days Past Due | Home equity loans serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	[1]	4	6
Financing Receivables 60 To 89 Days Past Due | Home equity lines of credit serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	[1]	5	6
Financing Receivables 60 To 89 Days Past Due | Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		31	32
Financing Receivables 60 To 89 Days Past Due | Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		11	11
Financing Receivables 60 To 89 Days Past Due | Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		8	9
Financing Receivables 60 To 89 Days Past Due | Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		4	4
Financing Receivables 60 To 89 Days Past Due | Total retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		105	116
Financing Receivables 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		931	849
Financing Receivables 90 Days or More Past Due | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		145	246
Financing Receivables 90 Days or More Past Due | Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		79	104
Financing Receivables 90 Days or More Past Due | Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		207	205
Financing Receivables 90 Days or More Past Due | Home equity loans serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	[1]	17	20
Financing Receivables 90 Days or More Past Due | Home equity lines of credit serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	[1]	35	29
Financing Receivables 90 Days or More Past Due | Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		37	35
Financing Receivables 90 Days or More Past Due | Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		42	41
Financing Receivables 90 Days or More Past Due | Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		14	16
Financing Receivables 90 Days or More Past Due | Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		4	5
Financing Receivables 90 Days or More Past Due | Total retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		$ 580	$ 701

[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.