SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Mortgage Servicing Rights (Details) - USD ($)	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Mortgage servicing rights
Classification of Securitizations
Fair value of capitalized mortgage servicing rights	$ 520,000,000	$ 433,000,000
Principal amount of loans and other financial instruments	58,000,000,000	52,000,000,000
Capitalized MSRs
Balance, at beginning of period	404,000,000	336,000,000
Originations	34,000,000	43,000,000
Changes in fair value of MSRs due to changes in inputs and assumptions	98,000,000	73,000,000
Other changes	(17,000,000)	(19,000,000)
Sale of MSRs	0	0
Balance, as of March 31	520,000,000	433,000,000
MSR fees
Servicing fees	29,000,000	31,000,000
Late fees	1,000,000	1,000,000
Ancillary fees	0	0
Total MSR fees	30,000,000	32,000,000
Mortgage securitizations - Non-agency-sponsored
Re-securitizations
Fair value of re-securitizations deals in which the entity holds a retained interest	0		$ 0
Mortgage securitizations - U.S. agency-sponsored
Re-securitizations
Fair value of re-securitizations deals in which the entity holds a retained interest	1,200,000,000		1,200,000,000
Securities transferred to re-securitization entities	9,300,000,000	$ 13,100,000,000
Market value of retained interest related to re-securitization transaction	300,000,000		641,000,000
Original fair value of re-securitizations deals in which the entity holds a retained interest	$ 80,300,000,000		$ 78,400,000,000