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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Commissions and fees
Administration and other fiduciary fees	$ 880	$ 911	$ 2,588	$ 2,750
Custody fees
Commissions and fees
Administration and other fiduciary fees	395	430	1,183	1,321
Custody fees | ICG
Commissions and fees
Administration and other fiduciary fees	370	371	1,115	1,138
Custody fees | GCB
Commissions and fees
Administration and other fiduciary fees	5	41	14	133
Custody fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	20	18	54	50
Fiduciary fees
Commissions and fees
Administration and other fiduciary fees	343	330	969	978
Fiduciary fees | ICG
Commissions and fees
Administration and other fiduciary fees	170	160	485	492
Fiduciary fees | GCB
Commissions and fees
Administration and other fiduciary fees	160	158	460	455
Fiduciary fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	13	12	24	31
Guarantee fees
Commissions and fees
Administration and other fiduciary fees	142	151	436	451
Guarantee fees | ICG
Commissions and fees
Administration and other fiduciary fees	126	136	388	403
Guarantee fees | GCB
Commissions and fees
Administration and other fiduciary fees	15	14	43	43
Guarantee fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	1	1	5	5
Administration and other fiduciary fees
Commissions and fees
Administration and other fiduciary fees	880	911	2,588	2,750
Revenue not accounted for under ASC 606, Revenue from Contracts with Customers	142	151	436	451
Administration and other fiduciary fees | ICG
Commissions and fees
Administration and other fiduciary fees	666	667	1,988	2,033
Administration and other fiduciary fees | GCB
Commissions and fees
Administration and other fiduciary fees	180	213	517	631
Administration and other fiduciary fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	$ 34	$ 31	$ 83	$ 86