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, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Total	$ 103,551	$ 99,042
Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	49,557	46,214
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	35,927	33,264
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	9,825	8,971
Leases
Financing Receivable, Recorded Investment [Line Items]
Total	3,805	3,979
Pass | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	46,815	43,606
Pass | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	33,931	31,276
Pass | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	9,281	8,450
Pass | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	3,603	3,880
Special Mention | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	1,253	1,238
Special Mention | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	855	911
Special Mention | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	318	272
Special Mention | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	80	55
Substandard | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	1,293	1,217
Substandard | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	1,015	1,002
Substandard | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	156	171
Substandard | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	122	44
Doubtful | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	196	153
Doubtful | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	126	75
Doubtful | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	70	78
Doubtful | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	$ 0	$ 0