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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Commissions and fees
Administration and other fiduciary fees	$ 819	$ 869	$ 1,673	$ 1,708
Custody fees
Commissions and fees
Administration and other fiduciary fees	399	405	788	788
Custody fees | ICG
Commissions and fees
Administration and other fiduciary fees	372	383	738	747
Custody fees | GCB
Commissions and fees
Administration and other fiduciary fees	6	4	14	7
Custody fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	21	18	36	34
Fiduciary fees
Commissions and fees
Administration and other fiduciary fees	290	316	618	626
Fiduciary fees | ICG
Commissions and fees
Administration and other fiduciary fees	158	162	330	314
Fiduciary fees | GCB
Commissions and fees
Administration and other fiduciary fees	132	154	288	300
Fiduciary fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	0	0	0	12
Guarantee fees
Commissions and fees
Administration and other fiduciary fees	130	148	267	294
Guarantee fees | ICG
Commissions and fees
Administration and other fiduciary fees	127	144	261	286
Guarantee fees | GCB
Commissions and fees
Administration and other fiduciary fees	1	2	3	4
Guarantee fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	2	2	3	4
Administration and other fiduciary fees
Commissions and fees
Administration and other fiduciary fees	819	869	1,673	1,708
Revenue not accounted for under ASC 606, revenue from contracts with customers	130	148	267	294
Administration and other fiduciary fees | ICG
Commissions and fees
Administration and other fiduciary fees	657	689	1,329	1,347
Administration and other fiduciary fees | GCB
Commissions and fees
Administration and other fiduciary fees	139	160	305	311
Administration and other fiduciary fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	$ 23	$ 20	$ 39	$ 50