COMMISSIONS AND FEES; ADMINISTRATION AND OTHER FIDUCIARY FEES - Administration and Other Fiduciary Fees (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Commissions and fees
Administration and other fiduciary fees	$ 1,007	$ 892	$ 2,990	$ 2,565
Custody fees
Commissions and fees
Administration and other fiduciary fees	479	437	1,439	1,225
Custody fees | ICG
Commissions and fees
Administration and other fiduciary fees	471	427	1,419	1,165
Custody fees | GCB
Commissions and fees
Administration and other fiduciary fees	7	8	19	22
Custody fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	1	2	1	38
Fiduciary fees
Commissions and fees
Administration and other fiduciary fees	382	320	1,113	938
Fiduciary fees | ICG
Commissions and fees
Administration and other fiduciary fees	204	167	596	497
Fiduciary fees | GCB
Commissions and fees
Administration and other fiduciary fees	175	153	511	441
Fiduciary fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	3	0	6	0
Guarantee fees
Commissions and fees
Administration and other fiduciary fees	146	135	438	402
Guarantee fees | ICG
Commissions and fees
Administration and other fiduciary fees	144	132	429	393
Guarantee fees | GCB
Commissions and fees
Administration and other fiduciary fees	1	2	5	5
Guarantee fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	1	1	4	4
Administration and other fiduciary fees
Commissions and fees
Administration and other fiduciary fees	1,007	892	2,990	2,565
Revenue not accounted for under ASC 606, revenue from contracts with customers	146	135	438	402
Administration and other fiduciary fees | ICG
Commissions and fees
Administration and other fiduciary fees	819	726	2,444	2,055
Administration and other fiduciary fees | GCB
Commissions and fees
Administration and other fiduciary fees	183	163	535	468
Administration and other fiduciary fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	$ 5	$ 3	$ 11	$ 42