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	Mar. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Total	$ 100,991	$ 99,042
Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	47,972	46,214
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	34,671	33,264
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	9,406	8,971
Leases
Financing Receivable, Recorded Investment [Line Items]
Total	3,895	3,979
Pass | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	45,198	43,606
Pass | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	32,567	31,276
Pass | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	8,864	8,450
Pass | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	3,767	3,880
Special Mention | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	1,272	1,238
Special Mention | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	928	911
Special Mention | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	272	272
Special Mention | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	72	55
Substandard | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	1,326	1,217
Substandard | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	1,086	1,002
Substandard | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	184	171
Substandard | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	56	44
Doubtful | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	176	153
Doubtful | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	90	75
Doubtful | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	86	78
Doubtful | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	$ 0	$ 0