SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Mortgage Servicing Rights (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Capitalized MSRs
Balance, beginning of period	$ 1,564
Balance, as of March 31	567
Mortgage servicing rights
Classification of Securitizations
Fair value of capitalized mortgage servicing rights	567		$ 1,600
Principal amount of loans and other financial instruments	71,000		168,000
Capitalized MSRs
Balance, beginning of period	1,564	$ 1,781
Originations	35	33
Changes in fair value of MSRs due to changes in inputs and assumptions	67	(225)
Other changes	(53)	(79)
Sale of MSRs	(1,046)	14
Balance, as of March 31	567	1,524
MSR fees
Servicing fees	106	128
Late fees	3	4
Ancillary fees	4	5
Total MSR fees	113	137
Mortgage securitizations - Non-agency-sponsored
Re-securitizations
Fair value of re-securitizations deals in which the entity holds a retained interest	126		126
Original par value of re-securitizations deals in which the entity holds a retained interest	1,000		1,300
U.S. government-sponsored agency guaranteed
Re-securitizations
Fair value of re-securitizations deals in which the entity holds a retained interest	2,300		2,300
Securities transferred to re-securitization entities	4,500	$ 7,300
Market value of retained interest related to re-securitization transaction	599		741
Original fair value of re-securitizations deals in which the entity holds a retained interest	$ 68,600		$ 71,800