ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Loans with Indicators of High Credit Risk (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
High loan-to-value
Financing Receivable, Recorded Investment [Line Items]
Investment in loan balance	$ 3,541	$ 5,433
High loan-to-value | Residential Mortgages
Financing Receivable, Recorded Investment [Line Items]
Investment in loan balance	773	1,054
High loan-to-value | Home Equity Loans and Lines of Credit
Financing Receivable, Recorded Investment [Line Items]
Investment in loan balance	1,743	2,798
High loan-to-value | Home Equity Products serviced by others
Financing Receivable, Recorded Investment [Line Items]
Investment in loan balance	1,025	1,581
High loan-to-value | Credit Cards
Financing Receivable, Recorded Investment [Line Items]
Investment in loan balance	0	0
Interest only/negative amortization
Financing Receivable, Recorded Investment [Line Items]
Investment in loan balance	894	882
Interest only/negative amortization | Residential Mortgages
Financing Receivable, Recorded Investment [Line Items]
Investment in loan balance	894	882
Interest only/negative amortization | Home Equity Loans and Lines of Credit
Financing Receivable, Recorded Investment [Line Items]
Investment in loan balance	0	0
Interest only/negative amortization | Home Equity Products serviced by others
Financing Receivable, Recorded Investment [Line Items]
Investment in loan balance	0	0
Interest only/negative amortization | Credit Cards
Financing Receivable, Recorded Investment [Line Items]
Investment in loan balance	0	0
Low introductory rate
Financing Receivable, Recorded Investment [Line Items]
Investment in loan balance	98	119
Low introductory rate | Residential Mortgages
Financing Receivable, Recorded Investment [Line Items]
Investment in loan balance	0	0
Low introductory rate | Home Equity Loans and Lines of Credit
Financing Receivable, Recorded Investment [Line Items]
Investment in loan balance	0	0
Low introductory rate | Home Equity Products serviced by others
Financing Receivable, Recorded Investment [Line Items]
Investment in loan balance	0	0
Low introductory rate | Credit Cards
Financing Receivable, Recorded Investment [Line Items]
Investment in loan balance	98	119
Multiple characteristics and other
Financing Receivable, Recorded Investment [Line Items]
Investment in loan balance	24	96
Multiple characteristics and other | Residential Mortgages
Financing Receivable, Recorded Investment [Line Items]
Investment in loan balance	24	96
Multiple characteristics and other | Home Equity Loans and Lines of Credit
Financing Receivable, Recorded Investment [Line Items]
Investment in loan balance	0	0
Multiple characteristics and other | Home Equity Products serviced by others
Financing Receivable, Recorded Investment [Line Items]
Investment in loan balance	0	0
Multiple characteristics and other | Credit Cards
Financing Receivable, Recorded Investment [Line Items]
Investment in loan balance	0	0
Credit Risk, Loan Products with Increased Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Investment in loan balance	4,557	6,530
Credit Risk, Loan Products with Increased Credit Exposure [Member] | Residential Mortgages
Financing Receivable, Recorded Investment [Line Items]
Investment in loan balance	1,691	2,032
Credit Risk, Loan Products with Increased Credit Exposure [Member] | Home Equity Loans and Lines of Credit
Financing Receivable, Recorded Investment [Line Items]
Investment in loan balance	1,743	2,798
Credit Risk, Loan Products with Increased Credit Exposure [Member] | Home Equity Products serviced by others
Financing Receivable, Recorded Investment [Line Items]
Investment in loan balance	1,025	1,581
Credit Risk, Loan Products with Increased Credit Exposure [Member] | Credit Cards
Financing Receivable, Recorded Investment [Line Items]
Investment in loan balance	$ 98	$ 119