LOANS - Corporate Troubled Debt Restructurings (Details) - Corporate - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Financing receivable impaired
Carrying Value	$ 236	$ 248	$ 307	$ 350
TDRs involving changes in the amount and/or timing of principal payments	32	73	32	73
TDRs involving changes in the amount and/or timing of interest payments	0	174	0	174
TDRs involving changes in the amount and/or timing of both principal and interest payments	204	1	$ 275	103
Period within which default occurred post-modification			1 year
Number of days past due, default status			60 days
Carrying Value	855	741	$ 855	741
TDR in payment default	3	7	15	7
Commercial and industrial
Financing receivable impaired
Carrying Value	233	105	288	203
TDRs involving changes in the amount and/or timing of principal payments	32	73	32	73
TDRs involving changes in the amount and/or timing of interest payments	0	32	0	32
TDRs involving changes in the amount and/or timing of both principal and interest payments	201	0	256	98
Carrying Value	591	323	591	323
TDR in payment default	3	7	12	7
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	0	24	0
TDR in payment default	0	0	3	0
Mortgage and real estate
Financing receivable impaired
Carrying Value	3	1	4	5
TDRs involving changes in the amount and/or timing of principal payments	0	0	0	0
TDRs involving changes in the amount and/or timing of interest payments	0	0	0	0
TDRs involving changes in the amount and/or timing of both principal and interest payments	3	1	4	5
Carrying Value	74	130	74	130
TDR in payment default	0	0	0	0
Other
Financing receivable impaired
Carrying Value		142		142
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		142		142
TDRs involving changes in the amount and/or timing of both principal and interest payments		0		0
Carrying Value	166	288	166	288
TDR in payment default	$ 0	$ 0	$ 0	$ 0
Commercial banking
Financing receivable impaired
Number of days past due, default status			90 days