ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Impaired Loans by Class (Details) - USD ($) $ in Millions		Mar. 31, 2016		Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance		$ 591		$ 641
Allowance on Impaired Loans		124		137
Impaired Loans Without a Related Allowance		623		742
Unpaid Contractual Balance		1,383		1,671
Total Recorded Investment in Impaired Loans		1,214		1,383
Other loans held for sale		386		40
TDR Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Other loans held for sale		373
Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance		219		148
Allowance on Impaired Loans		42		36
Impaired Loans Without a Related Allowance		220		70
Unpaid Contractual Balance		483		214
Total Recorded Investment in Impaired Loans		439		218
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance		163		92
Allowance on Impaired Loans		30		23
Impaired Loans Without a Related Allowance		208		58
Unpaid Contractual Balance		414		144
Total Recorded Investment in Impaired Loans		371		150
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance		56		56
Allowance on Impaired Loans		12		13
Impaired Loans Without a Related Allowance		12		12
Unpaid Contractual Balance		69		70
Total Recorded Investment in Impaired Loans		68		68
Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance		372		493
Allowance on Impaired Loans		82		101
Impaired Loans Without a Related Allowance		403		672
Unpaid Contractual Balance		900		1,457
Total Recorded Investment in Impaired Loans		775		1,165
Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance		35	[1]	121
Allowance on Impaired Loans		4	[1]	16
Impaired Loans Without a Related Allowance		111	[1]	320
Unpaid Contractual Balance		183	[1]	608
Total Recorded Investment in Impaired Loans		146	[1]	441
Residential mortgages | TDR Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Other loans held for sale		288
Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance		55	[1]	85
Allowance on Impaired Loans		6	[1]	11
Impaired Loans Without a Related Allowance		84	[1]	139
Unpaid Contractual Balance		165	[1]	283
Total Recorded Investment in Impaired Loans		139	[1]	224
Home equity loans | TDR Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Other loans held for sale		85
Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance		25		27
Allowance on Impaired Loans		3		2
Impaired Loans Without a Related Allowance		165		167
Unpaid Contractual Balance		227		234
Total Recorded Investment in Impaired Loans		190		194
Home equity loans serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance	[2]	48		50
Allowance on Impaired Loans	[2]	7		8
Impaired Loans Without a Related Allowance	[2]	22		24
Unpaid Contractual Balance	[2]	84		88
Total Recorded Investment in Impaired Loans	[2]	70		74
Home equity lines of credit serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance	[2]	3		3
Allowance on Impaired Loans	[2]	0		1
Impaired Loans Without a Related Allowance	[2]	7		7
Unpaid Contractual Balance	[2]	14		14
Total Recorded Investment in Impaired Loans	[2]	10		10
Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance		3		3
Allowance on Impaired Loans		0		0
Impaired Loans Without a Related Allowance		11		11
Unpaid Contractual Balance		19		19
Total Recorded Investment in Impaired Loans		14		14
Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance		163		163
Allowance on Impaired Loans		47		48
Impaired Loans Without a Related Allowance		1		2
Unpaid Contractual Balance		164		165
Total Recorded Investment in Impaired Loans		164		165
Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance		27		28
Allowance on Impaired Loans		11		11
Impaired Loans Without a Related Allowance		0		0
Unpaid Contractual Balance		27		28
Total Recorded Investment in Impaired Loans		27		28
Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance		13		13
Allowance on Impaired Loans		4		4
Impaired Loans Without a Related Allowance		2		2
Unpaid Contractual Balance		17		18
Total Recorded Investment in Impaired Loans		$ 15		$ 15

[1] Excluded from the table above are retail TDR principal balances held for sale with a total recorded investment of $373 million, including residential mortgages of $288 million and home equity loans of $85 million.

[2] 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.