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, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Total	$ 109,046	$ 107,669
Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	51,888	51,651
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	37,329	37,274
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	11,213	10,624
Leases
Financing Receivable, Recorded Investment [Line Items]
Total	3,346	3,753
Pass | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	49,152	48,739
Pass | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	35,259	35,010
Pass | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	10,678	10,146
Pass | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	3,215	3,583
Special Mention | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	1,720	1,437
Special Mention | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	1,169	1,015
Special Mention | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	444	370
Special Mention | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	107	52
Substandard | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	699	1,188
Substandard | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	622	1,027
Substandard | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	53	58
Substandard | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	24	103
Doubtful | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Total	317	287
Doubtful | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	279	222
Doubtful | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	38	50
Doubtful | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	$ 0	$ 15