FEDERAL FUNDS, SECURITIES BORROWED, LOANED AND SUBJECT TO REPURCHASE AGREEMENTS - Repurchase Agreements (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	$ 195,318	$ 203,543
Security lending agreements	19,924	25,900
Gross amounts of recognized liabilities	215,242	$ 229,443
U.S. Treasury and federal agency securities
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	75,722
Security lending agreements	21
Gross amounts of recognized liabilities	75,743
State and municipal securities
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	629
Security lending agreements	0
Gross amounts of recognized liabilities	629
Foreign government
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	59,532
Security lending agreements	619
Gross amounts of recognized liabilities	60,151
Corporate
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	15,859
Security lending agreements	1,155
Gross amounts of recognized liabilities	17,014
Equity securities
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	10,762
Security lending agreements	18,060
Gross amounts of recognized liabilities	28,822
Mortgage-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	23,217
Security lending agreements	0
Gross amounts of recognized liabilities	23,217
Asset-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	4,498
Security lending agreements	0
Gross amounts of recognized liabilities	4,498
Other debt securities
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	5,099
Security lending agreements	69
Gross amounts of recognized liabilities	5,168
Open and Overnight
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	105,497
Security lending agreements	13,572
Gross amounts of recognized liabilities	119,069
Up to 30 Days
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	48,454
Security lending agreements	2,482
Gross amounts of recognized liabilities	50,936
31-90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	17,420
Security lending agreements	2,019
Gross amounts of recognized liabilities	19,439
Greater than 90 days
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	23,947
Security lending agreements	1,851
Gross amounts of recognized liabilities	$ 25,798