SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Mortgage Servicing Rights (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Capitalized MSRs
Balance, at beginning of period			$ 1,564
Balance, as of September 30	$ 553		553
Mortgage servicing rights
Classification of Securitizations
Fair value of capitalized mortgage servicing rights	553	$ 1,300	553	$ 1,300
Principal amount of loans and other financial instruments	68,000	173,000	68,000	173,000
Capitalized MSRs
Balance, at beginning of period	560	1,324	1,564	1,781
Originations	19	43	75	111
Changes in fair value of MSRs due to changes in inputs and assumptions	(6)	13	50	(349)
Other changes	(20)	(78)	(90)	(255)
Sale of MSRs	0	(32)	(1,046)	(18)
Balance, as of September 30	553	1,270	553	1,270
MSR fees
Servicing fees	65	117	236	371
Late fees	2	3	8	11
Ancillary fees	3	4	11	13
Total MSR fees	70	124	255	395
Mortgage securitizations - Non-agency-sponsored
Re-securitizations
Fair value of re-securitizations deals in which the entity holds a retained interest	75		75		$ 126
Original par value of re-securitizations deals in which the entity holds a retained interest	954		954		1,300
U.S. government-sponsored agency guaranteed
Re-securitizations
Fair value of re-securitizations deals in which the entity holds a retained interest	2,000		2,000		2,300
Securities transferred to re-securitization entities	9,900	$ 7,100	20,000	$ 21,300
Market value of retained interest related to re-securitization transaction	713		713		741
Original fair value of re-securitizations deals in which the entity holds a retained interest	$ 67,600		$ 67,600		$ 71,800