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, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Total	$ 108,111	$ 107,669
Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	51,892	51,651
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	37,369	37,274
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	10,915	10,624
Leases
Financing Receivable, Recorded Investment [Line Items]
Total	3,608	3,753
Pass | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	49,055	48,739
Pass | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	35,125	35,010
Pass | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	10,483	10,146
Pass | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	3,447	3,583
Special Mention | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	1,514	1,437
Special Mention | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	1,129	1,015
Special Mention | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	330	370
Special Mention | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	55	52
Substandard | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	969	1,188
Substandard | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	807	1,027
Substandard | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	56	58
Substandard | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	106	103
Doubtful | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	354	287
Doubtful | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	308	222
Doubtful | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	46	50
Doubtful | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	$ 0	$ 15