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	Sep. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Total	$ 97,431	$ 93,410
Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	45,269	43,226
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	32,726	31,431
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	8,678	7,809
Leases
Financing Receivable, Recorded Investment [Line Items]
Total	3,865	3,986
Pass | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	43,127	41,300
Pass | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	31,005	30,022
Pass | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	8,326	7,354
Pass | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	3,796	3,924
Special Mention | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	1,153	1,217
Special Mention | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	924	876
Special Mention | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	207	329
Special Mention | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	22	12
Substandard | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	862	538
Substandard | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	712	427
Substandard | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	103	61
Substandard | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	47	50
Doubtful | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	127	171
Doubtful | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	85	106
Doubtful | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	42	65
Doubtful | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	$ 0	$ 0