ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Recorded Investment in Commercial Loans and Leases by Regulatory Classification Ratings (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Total	$ 110,151	$ 107,669
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	52,381	51,651
Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total	49,201	48,739
Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total	1,955	1,437
Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total	937	1,188
Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total	288	287
Commercial | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total	37,706	37,274
Commercial | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total	35,309	35,010
Commercial | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total	1,368	1,015
Commercial | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total	770	1,027
Commercial | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total	259	222
Commercial | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total	11,426	10,624
Commercial | Commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Total	10,737	10,146
Commercial | Commercial real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total	514	370
Commercial | Commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total	146	58
Commercial | Commercial real estate | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total	29	50
Commercial | Leases
Financing Receivable, Recorded Investment [Line Items]
Total	3,249	3,753
Commercial | Leases | Pass
Financing Receivable, Recorded Investment [Line Items]
Total	3,155	3,583
Commercial | Leases | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total	73	52
Commercial | Leases | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total	21	103
Commercial | Leases | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total	$ 0	$ 15