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, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Commissions and fees
Administration and other fiduciary fees	$ 1,022	$ 819	$ 1,983	$ 1,673
Custody fees
Commissions and fees
Administration and other fiduciary fees	503	399	960	788
Custody fees | ICG
Commissions and fees
Administration and other fiduciary fees	497	372	948	738
Custody fees | GCB
Commissions and fees
Administration and other fiduciary fees	6	6	12	14
Custody fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	0	21	0	36
Fiduciary fees
Commissions and fees
Administration and other fiduciary fees	372	290	731	618
Fiduciary fees | ICG
Commissions and fees
Administration and other fiduciary fees	200	158	392	330
Fiduciary fees | GCB
Commissions and fees
Administration and other fiduciary fees	169	132	336	288
Fiduciary fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	3	0	3	0
Guarantee fees
Commissions and fees
Administration and other fiduciary fees	147	130	292	267
Guarantee fees | ICG
Commissions and fees
Administration and other fiduciary fees	143	127	285	261
Guarantee fees | GCB
Commissions and fees
Administration and other fiduciary fees	2	1	4	3
Guarantee fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	2	2	3	3
Administration and other fiduciary fees
Commissions and fees
Administration and other fiduciary fees	1,022	819	1,983	1,673
Revenue not accounted for under ASC 606, revenue from contracts with customers	147	130	292	267
Administration and other fiduciary fees | ICG
Commissions and fees
Administration and other fiduciary fees	840	657	1,625	1,329
Administration and other fiduciary fees | GCB
Commissions and fees
Administration and other fiduciary fees	177	139	352	305
Administration and other fiduciary fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	$ 5	$ 23	$ 6	$ 39