ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Accruing and Nonaccruing Past Due Amounts (Details) - Loans and Leases - USD ($) $ in Millions		Mar. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		$ 1,409	$ 1,356
Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		450	204
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		307	84
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		128	110
Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		15	10
Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		959	1,152
Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		210	316
Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		111	148
Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		276	285
Home equity loans serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	[1]	35	40
Home equity lines of credit serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	[1]	49	45
Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		160	194
Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		71	71
Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		33	36
Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		14	17
Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		362	383
Financing Receivables, 30 to 59 Days Past Due | Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		68	48
Financing Receivables, 30 to 59 Days Past Due | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		13	9
Financing Receivables, 30 to 59 Days Past Due | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		40	30
Financing Receivables, 30 to 59 Days Past Due | Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		15	9
Financing Receivables, 30 to 59 Days Past Due | Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		294	335
Financing Receivables, 30 to 59 Days Past Due | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		52	54
Financing Receivables, 30 to 59 Days Past Due | Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		26	32
Financing Receivables, 30 to 59 Days Past Due | Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		53	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]	14	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]	9	10
Financing Receivables, 30 to 59 Days Past Due | Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		104	127
Financing Receivables, 30 to 59 Days Past Due | Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		17	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		9	8
Financing Receivables 60 To 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		80	124
Financing Receivables 60 To 89 Days Past Due | Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		7	8
Financing Receivables 60 To 89 Days Past Due | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		7	4
Financing Receivables 60 To 89 Days Past Due | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		0	3
Financing Receivables 60 To 89 Days Past Due | Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		0	1
Financing Receivables 60 To 89 Days Past Due | Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		73	116
Financing Receivables 60 To 89 Days Past Due | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		7	16
Financing Receivables 60 To 89 Days Past Due | Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		5	12
Financing Receivables 60 To 89 Days Past Due | Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		17	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]	1	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		20	32
Financing Receivables 60 To 89 Days Past Due | Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		9	11
Financing Receivables 60 To 89 Days Past Due | Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		7	9
Financing Receivables 60 To 89 Days Past Due | Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		2	4
Financing Receivables 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		967	849
Financing Receivables 90 Days or More Past Due | Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		375	148
Financing Receivables 90 Days or More Past Due | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		287	71
Financing Receivables 90 Days or More Past Due | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		88	77
Financing Receivables 90 Days or More Past Due | Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		0	0
Financing Receivables 90 Days or More Past Due | Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		592	701
Financing Receivables 90 Days or More Past Due | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		151	246
Financing Receivables 90 Days or More Past Due | Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		80	104
Financing Receivables 90 Days or More Past Due | Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		206	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]	20	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		36	35
Financing Receivables 90 Days or More Past Due | Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		45	41
Financing Receivables 90 Days or More Past Due | Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		16	16
Financing Receivables 90 Days or More Past Due | Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		$ 3	$ 5

[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.