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	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Total	$ 99,042	$ 93,410
Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	46,214	43,226
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	33,264	31,431
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	8,971	7,809
Leases
Financing Receivable, Recorded Investment [Line Items]
Total	3,979	3,986
Pass | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	43,606	41,300
Pass | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	31,276	30,022
Pass | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	8,450	7,354
Pass | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	3,880	3,924
Special Mention | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	1,238	1,217
Special Mention | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	911	876
Special Mention | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	272	329
Special Mention | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	55	12
Substandard | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	1,217	538
Substandard | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	1,002	427
Substandard | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	171	61
Substandard | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	44	50
Doubtful | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	153	171
Doubtful | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	75	106
Doubtful | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	78	65
Doubtful | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	$ 0	$ 0