FEDERAL FUNDS, SECURITIES BORROWED, LOANED AND SUBJECT TO REPURCHASE AGREEMENTS - Repurchase Agreements (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Assets Sold under Agreements to Repurchase
Securities sold under agreements to repurchase	$ 257,900	$ 216,122
Deposits received for securities loaned	13,811	13,305
Total	271,711	229,427
U.S. Treasury and federal agency securities
Assets Sold under Agreements to Repurchase
Securities sold under agreements to repurchase	95,116	58,774
Deposits received for securities loaned	110	0
Total	95,226	58,774
State and municipal securities
Assets Sold under Agreements to Repurchase
Securities sold under agreements to repurchase	2,803	1,605
Deposits received for securities loaned	0	0
Total	2,803	1,605
Foreign government
Assets Sold under Agreements to Repurchase
Securities sold under agreements to repurchase	94,306	89,576
Deposits received for securities loaned	301	105
Total	94,607	89,681
Corporate bonds
Assets Sold under Agreements to Repurchase
Securities sold under agreements to repurchase	22,247	20,194
Deposits received for securities loaned	545	657
Total	22,792	20,851
Equity securities
Assets Sold under Agreements to Repurchase
Securities sold under agreements to repurchase	18,759	20,724
Deposits received for securities loaned	11,982	11,907
Total	30,741	32,631
Mortgage-backed securities
Assets Sold under Agreements to Repurchase
Securities sold under agreements to repurchase	15,088	17,791
Deposits received for securities loaned	0	0
Total	15,088	17,791
Asset-backed securities
Assets Sold under Agreements to Repurchase
Securities sold under agreements to repurchase	6,513	5,479
Deposits received for securities loaned	0	0
Total	6,513	5,479
Other
Assets Sold under Agreements to Repurchase
Securities sold under agreements to repurchase	3,068	1,979
Deposits received for securities loaned	873	636
Total	3,941	2,615
Open and overnight
Assets Sold under Agreements to Repurchase
Securities sold under agreements to repurchase	121,109	82,073
Deposits received for securities loaned	7,091	9,946
Total	128,200	92,019
Up to 30 days
Assets Sold under Agreements to Repurchase
Securities sold under agreements to repurchase	59,246	68,372
Deposits received for securities loaned	307	266
Total	59,553	68,638
31–90 days
Assets Sold under Agreements to Repurchase
Securities sold under agreements to repurchase	30,558	33,846
Deposits received for securities loaned	3,200	1,912
Total	33,758	35,758
Greater than 90 days
Assets Sold under Agreements to Repurchase
Securities sold under agreements to repurchase	46,987	31,831
Deposits received for securities loaned	3,213	1,181
Total	$ 50,200	$ 33,012