LOANS - Corporate Troubled Debt Restructurings (Details) - Corporate - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Financing receivable impaired
Carrying Value	$ 71	$ 102
TDRs involving changes in the amount and/or timing of principal payments	0	0
TDRs involving changes in the amount and/or timing of interest payments	0	0
TDRs involving changes in the amount and/or timing of both principal and interest payments	$ 71	102
Period within which default occurred post-modification	1 year
Number of days past due, default status	60 days
Carrying Value	$ 675	663
TDR in payment default	12	0
Commercial and industrial
Financing receivable impaired
Carrying Value	55	98
TDRs involving changes in the amount and/or timing of principal payments	0	0
TDRs involving changes in the amount and/or timing of interest payments	0	0
TDRs involving changes in the amount and/or timing of both principal and interest payments	55	98
Carrying Value	390	219
TDR in payment default	9	0
Loans to financial institutions
Financing receivable impaired
Carrying Value	15
TDRs involving changes in the amount and/or timing of principal payments	0
TDRs involving changes in the amount and/or timing of interest payments	0
TDRs involving changes in the amount and/or timing of both principal and interest payments	15
Carrying Value	24	2
TDR in payment default	3	0
Mortgage and real estate
Financing receivable impaired
Carrying Value	1	4
TDRs involving changes in the amount and/or timing of principal payments	0	0
TDRs involving changes in the amount and/or timing of interest payments	0	0
TDRs involving changes in the amount and/or timing of both principal and interest payments	1	4
Carrying Value	84	139
TDR in payment default	$ 0	0
Commercial banking loans
Financing receivable impaired
Number of days past due, default status	90 days
Other
Financing receivable impaired
Carrying Value	$ 177	303
TDR in payment default	$ 0	$ 0