SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Mortgage Servicing Rights (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Capitalized MSRs
Balance at beginning of period			$ 1,845
Balance at end of period	$ 1,924		1,924
Mortgage servicing rights
Classification of Securitizations
Fair value of capitalized mortgage servicing rights	1,900	$ 2,300	1,900	$ 2,300
Principal amount of loans and other financial instruments	209,000	250,000	209,000	250,000
Capitalized MSRs
Balance at beginning of period	1,685	2,586	1,845	2,718
Originations	68	49	111	99
Changes in fair value of MSRs due to changes in inputs and assumptions	262	(91)	191	(175)
Other changes	(82)	(99)	(182)	(225)
Sale of MSRs	(9)	(163)	(41)	(135)
Balance at end of period	1,924	2,282	1,924	2,282
MSR fees
Servicing fees	141	162	281	332
Late fees	4	5	8	15
Ancillary fees	15	16	22	36
Total MSR fees	160	183	311	383
Mortgage securitizations - Non-agency-sponsored
Re-securitizations
Original par value of securities transferred to re-securitization entities	195	251	649	389
Fair value of re-securitizations deals in which the entity holds a retained interest	435		435		$ 545
Market value of retained interest related to re-securitization transaction	79		79		194
Original par value of re-securitizations deals in which the entity holds a retained interest	5,200		5,200		5,100
Senior interests
Re-securitizations
Fair value of re-securitizations deals in which the entity holds a retained interest	29		29		133
Subordinated interests
Re-securitizations
Fair value of re-securitizations deals in which the entity holds a retained interest	406		406		412
U.S. government-sponsored agency guaranteed
Re-securitizations
Fair value of re-securitizations deals in which the entity holds a retained interest	2,100		2,100		1,800
Market value of retained interest related to re-securitization transaction	1,600		1,600		1,500
Securities transferred to re-securitization entities	4,600	4,900	8,900	11,300
Original fair value of re-securitizations deals in which the entity holds a retained interest	69,000		69,000		$ 73,000
Citicorp | Mortgage servicing rights
Classification of Securitizations
Fair value of capitalized mortgage servicing rights	$ 1,800	$ 1,800	$ 1,800	$ 1,800