SECURITIES BORROWED, LOANED AND SUBJECT TO REPURCHASE AGREEMENTS - Securities (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Federal Funds Purchased and Securities Sold under Agreements to Repurchase [Abstract]
Securities purchased under agreements to resell	$ 209,300	$ 204,655
Deposits paid for securities borrowed	99,755	90,067
Total, net	309,055	294,722
Allowance for credit losses on securities purchased and borrowed	(8)	(10)
Total, net of allowance	309,047	294,712
Securities sold under agreements to repurchase	198,353	181,194
Deposits received for securities loaned	23,464	18,331
Total, net	221,817	199,525
Securities-for-securities lending transactions	$ 3,300	$ 6,800