COMMISSIONS AND FEES; ADMINISTRATION AND OTHER FIDUCIARY FEES - Administration and Other Fiduciary Fees (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Commissions and fees
Administration and other fiduciary fees	$ 3,472	$ 3,411	$ 3,580
Custody fees
Commissions and fees
Administration and other fiduciary fees	1,657	1,542	1,695
Fiduciary fees
Commissions and fees
Administration and other fiduciary fees	1,274	1,296	1,285
Guarantee fees
Commissions and fees
Administration and other fiduciary fees	541	573	600
Administration and other fiduciary fees
Commissions and fees
Administration and other fiduciary fees	3,472	3,411	3,580
Revenue not accounted for under ASC 606	541	573	600
ICG | Custody fees
Commissions and fees
Administration and other fiduciary fees	1,590	1,453	1,497
ICG | Fiduciary fees
Commissions and fees
Administration and other fiduciary fees	668	647	645
ICG | Guarantee fees
Commissions and fees
Administration and other fiduciary fees	529	558	584
ICG | Administration and other fiduciary fees
Commissions and fees
Administration and other fiduciary fees	2,787	2,658	2,726
GCB | Custody fees
Commissions and fees
Administration and other fiduciary fees	29	16	133
GCB | Fiduciary fees
Commissions and fees
Administration and other fiduciary fees	602	621	597
GCB | Guarantee fees
Commissions and fees
Administration and other fiduciary fees	7	8	9
GCB | Administration and other fiduciary fees
Commissions and fees
Administration and other fiduciary fees	638	645	739
Corporate/Other | Custody fees
Commissions and fees
Administration and other fiduciary fees	38	73	65
Corporate/Other | Fiduciary fees
Commissions and fees
Administration and other fiduciary fees	4	28	43
Corporate/Other | Guarantee fees
Commissions and fees
Administration and other fiduciary fees	5	7	7
Corporate/Other | Administration and other fiduciary fees
Commissions and fees
Administration and other fiduciary fees	$ 47	$ 108	$ 115