ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Loans with Indicators of High Credit Risk (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
High loan-to-value
Financing Receivable, Recorded Investment [Line Items]
Total	$ 2,029	$ 2,472
High loan-to-value | Residential Mortgages
Financing Receivable, Recorded Investment [Line Items]
Total	519	649
High loan-to-value | Home Equity Loans and Lines of Credit
Financing Receivable, Recorded Investment [Line Items]
Total	815	1,038
High loan-to-value | Home Equity Products Serviced by Others
Financing Receivable, Recorded Investment [Line Items]
Total	695	785
High loan-to-value | Credit Cards
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
High loan-to-value | Student
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Interest only/negative amortization
Financing Receivable, Recorded Investment [Line Items]
Total	1,182	1,110
Interest only/negative amortization | Residential Mortgages
Financing Receivable, Recorded Investment [Line Items]
Total	1,181	1,110
Interest only/negative amortization | Home Equity Loans and Lines of Credit
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Interest only/negative amortization | Home Equity Products Serviced by Others
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Interest only/negative amortization | Credit Cards
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Interest only/negative amortization | Student
Financing Receivable, Recorded Investment [Line Items]
Total	1	0
Low introductory rate
Financing Receivable, Recorded Investment [Line Items]
Total	93	99
Low introductory rate | Residential Mortgages
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Low introductory rate | Home Equity Loans and Lines of Credit
Financing Receivable, Recorded Investment [Line Items]
Total	0	3
Low introductory rate | Home Equity Products Serviced by Others
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Low introductory rate | Credit Cards
Financing Receivable, Recorded Investment [Line Items]
Total	93	96
Low introductory rate | Student
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Multiple characteristics and other
Financing Receivable, Recorded Investment [Line Items]
Total	4	14
Multiple characteristics and other | Residential Mortgages
Financing Receivable, Recorded Investment [Line Items]
Total	4	14
Multiple characteristics and other | Home Equity Loans and Lines of Credit
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Multiple characteristics and other | Home Equity Products Serviced by Others
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Multiple characteristics and other | Credit Cards
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Multiple characteristics and other | Student
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Credit risk, loans with increased credit exposure
Financing Receivable, Recorded Investment [Line Items]
Total	3,308	3,695
Credit risk, loans with increased credit exposure | Residential Mortgages
Financing Receivable, Recorded Investment [Line Items]
Total	1,704	1,773
Credit risk, loans with increased credit exposure | Home Equity Loans and Lines of Credit
Financing Receivable, Recorded Investment [Line Items]
Total	815	1,041
Credit risk, loans with increased credit exposure | Home Equity Products Serviced by Others
Financing Receivable, Recorded Investment [Line Items]
Total	695	785
Credit risk, loans with increased credit exposure | Credit Cards
Financing Receivable, Recorded Investment [Line Items]
Total	93	96
Credit risk, loans with increased credit exposure | Student
Financing Receivable, Recorded Investment [Line Items]
Total	$ 1	$ 0