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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Commissions and fees
Administration and other fiduciary fees	$ 892	$ 880	$ 2,565	$ 2,588
Custody fees
Commissions and fees
Administration and other fiduciary fees	437	395	1,225	1,183
Custody fees | ICG
Commissions and fees
Administration and other fiduciary fees	427	370	1,165	1,117
Custody fees | GCB
Commissions and fees
Administration and other fiduciary fees	8	5	22	12
Custody fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	2	20	38	54
Fiduciary fees
Commissions and fees
Administration and other fiduciary fees	320	343	938	969
Fiduciary fees | ICG
Commissions and fees
Administration and other fiduciary fees	167	171	497	485
Fiduciary fees | GCB
Commissions and fees
Administration and other fiduciary fees	153	160	441	460
Fiduciary fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	0	12	0	24
Guarantee fees
Commissions and fees
Administration and other fiduciary fees	135	142	402	436
Guarantee fees | ICG
Commissions and fees
Administration and other fiduciary fees	132	139	393	425
Guarantee fees | GCB
Commissions and fees
Administration and other fiduciary fees	2	2	5	6
Guarantee fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	1	1	4	5
Administration and other fiduciary fees
Commissions and fees
Administration and other fiduciary fees	892	880	2,565	2,588
Revenue not accounted for under ASC 606, revenue from contracts with customers	135	142	402	436
Administration and other fiduciary fees | ICG
Commissions and fees
Administration and other fiduciary fees	726	680	2,055	2,027
Administration and other fiduciary fees | GCB
Commissions and fees
Administration and other fiduciary fees	163	167	468	478
Administration and other fiduciary fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	$ 3	$ 33	$ 42	$ 83