SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Mortgage Servicing Rights (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Capitalized MSRs
Balance, at beginning of period			$ 1,564
Balance, as of June 30	$ 560		560
Mortgage servicing rights
Classification of Securitizations
Fair value of capitalized mortgage servicing rights	560	$ 1,300	560	$ 1,300
Principal amount of loans and other financial instruments	135,000	186,000	135,000	186,000
Capitalized MSRs
Balance, at beginning of period	567	1,524	1,564	1,781
Originations	21	35	56	68
Changes in fair value of MSRs due to changes in inputs and assumptions	(11)	(137)	56	(362)
Other changes	(17)	(98)	(70)	(177)
Sale of MSRs	0	0	(1,046)	14
Balance, as of June 30	560	1,324	560	1,324
MSR fees
Servicing fees	65	126	171	254
Late fees	3	4	6	8
Ancillary fees	4	4	8	9
Total MSR fees	72	134	185	271
Mortgage securitizations - Non-agency-sponsored
Re-securitizations
Fair value of re-securitizations deals in which the entity holds a retained interest	112		112		$ 126
Original par value of re-securitizations deals in which the entity holds a retained interest	1,100		1,100		1,300
U.S. government-sponsored agency guaranteed
Re-securitizations
Fair value of re-securitizations deals in which the entity holds a retained interest	2,500		2,500		2,300
Securities transferred to re-securitization entities	5,600	$ 6,900	10,100	$ 14,200
Market value of retained interest related to re-securitization transaction	1,000		1,000		741
Original fair value of re-securitizations deals in which the entity holds a retained interest	$ 68,900		$ 68,900		$ 71,800