COMMISSIONS AND FEES; ADMINISTRATION AND OTHER FIDUCIARY FEES - Administration and Other Fiduciary Fees (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Commissions and fees
Administration and other fiduciary fees	$ 869	$ 934	$ 1,708	$ 1,839
Custody fees
Commissions and fees
Administration and other fiduciary fees	405	461	788	891
Custody fees | ICG
Commissions and fees
Administration and other fiduciary fees	381	399	745	767
Custody fees | GCB
Commissions and fees
Administration and other fiduciary fees	6	45	9	92
Custody fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	18	17	34	32
Fiduciary fees
Commissions and fees
Administration and other fiduciary fees	316	327	626	648
Fiduciary fees | ICG
Commissions and fees
Administration and other fiduciary fees	163	165	315	332
Fiduciary fees | GCB
Commissions and fees
Administration and other fiduciary fees	154	150	300	297
Fiduciary fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	(1)	12	11	19
Guarantee fees
Commissions and fees
Administration and other fiduciary fees	148	146	294	300
Guarantee fees | ICG
Commissions and fees
Administration and other fiduciary fees	132	130	262	267
Guarantee fees | GCB
Commissions and fees
Administration and other fiduciary fees	14	14	28	29
Guarantee fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	2	2	4	4
Administration and other fiduciary fees
Commissions and fees
Administration and other fiduciary fees	869	934	1,708	1,839
Revenue not accounted for under ASC 606, Revenue from Contracts with Customers	148	146	294	300
Administration and other fiduciary fees | ICG
Commissions and fees
Administration and other fiduciary fees	676	694	1,322	1,366
Administration and other fiduciary fees | GCB
Commissions and fees
Administration and other fiduciary fees	174	209	337	418
Administration and other fiduciary fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	$ 19	$ 31	$ 49	$ 55