COMMISSIONS AND FEES; ADMINISTRATION AND OTHER FIDUCIARY FEES - Administration and Other Fiduciary Fees (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Commissions and fees
Administration and other fiduciary fees	$ 839	$ 905
Custody fees
Commissions and fees
Administration and other fiduciary fees	383	431
Custody fees | ICG
Commissions and fees
Administration and other fiduciary fees	364	368
Custody fees | GCB
Commissions and fees
Administration and other fiduciary fees	3	47
Custody fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	16	16
Fiduciary fees
Commissions and fees
Administration and other fiduciary fees	310	321
Fiduciary fees | ICG
Commissions and fees
Administration and other fiduciary fees	152	167
Fiduciary fees | GCB
Commissions and fees
Administration and other fiduciary fees	146	147
Fiduciary fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	12	7
Guarantee fees
Commissions and fees
Administration and other fiduciary fees	146	153
Guarantee fees | ICG
Commissions and fees
Administration and other fiduciary fees	130	137
Guarantee fees | GCB
Commissions and fees
Administration and other fiduciary fees	14	14
Guarantee fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	2	2
Administration and other fiduciary fees
Commissions and fees
Administration and other fiduciary fees	839	905
Revenue not accounted for under ASC 606, Revenue from Contracts with Customers	146	153
Administration and other fiduciary fees | ICG
Commissions and fees
Administration and other fiduciary fees	646	672
Administration and other fiduciary fees | GCB
Commissions and fees
Administration and other fiduciary fees	163	208
Administration and other fiduciary fees | Corporate/Other
Commissions and fees
Administration and other fiduciary fees	$ 30	$ 25