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, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Total	$ 105,467	$ 99,042
Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	50,389	46,214
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	36,449	33,264
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	10,152	8,971
Leases
Financing Receivable, Recorded Investment [Line Items]
Total	3,788	3,979
Pass | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	47,499	43,606
Pass | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	34,245	31,276
Pass | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	9,646	8,450
Pass | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	3,608	3,880
Special Mention | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	1,291	1,238
Special Mention | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	883	911
Special Mention | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	355	272
Special Mention | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	53	55
Substandard | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	1,349	1,217
Substandard | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	1,138	1,002
Substandard | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	89	171
Substandard | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	122	44
Doubtful | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	250	153
Doubtful | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	183	75
Doubtful | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	62	78
Doubtful | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	$ 5	$ 0