ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Recorded Investment in Commercial Loans and Leases by Regulatory Classification Ratings (Details) - Loans and Leases - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Total	$ 96,538	$ 93,410
Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	45,068	43,226
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	33,027	31,431
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	8,157	7,809
Leases
Financing Receivable, Recorded Investment [Line Items]
Total	3,884	3,986
Pass | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	43,223	41,300
Pass | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	31,443	30,022
Pass | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	7,949	7,354
Pass | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	3,831	3,924
Special Mention | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	1,002	1,217
Special Mention | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	865	876
Special Mention | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	133	329
Special Mention | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	4	12
Substandard | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	718	538
Substandard | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	635	427
Substandard | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	34	61
Substandard | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	49	50
Doubtful | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	125	171
Doubtful | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	84	106
Doubtful | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	41	65
Doubtful | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	$ 0	$ 0