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	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Total	$ 107,669	$ 99,042
Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	51,651	46,214
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	37,274	33,264
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	10,624	8,971
Leases
Financing Receivable, Recorded Investment [Line Items]
Total	3,753	3,979
Pass | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	48,739	43,606
Pass | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	35,010	31,276
Pass | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	10,146	8,450
Pass | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	3,583	3,880
Special Mention | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	1,437	1,238
Special Mention | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	1,015	911
Special Mention | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	370	272
Special Mention | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	52	55
Substandard | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	1,188	1,217
Substandard | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	1,027	1,002
Substandard | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	58	171
Substandard | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	103	44
Doubtful | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	287	153
Doubtful | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	222	75
Doubtful | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	50	78
Doubtful | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	$ 15	$ 0