SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Mortgage Servicing Rights (Details) - USD ($)	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Mortgage servicing rights
Classification of Securitizations
Fair value of capitalized mortgage servicing rights	$ 433,000,000	$ 367,000,000
Principal amount of loans and other financial instruments	52,000,000,000	59,000,000,000
Capitalized MSRs
Balance, at beginning of period	336,000,000	495,000,000
Originations	43,000,000	32,000,000
Changes in fair value of MSRs due to changes in inputs and assumptions	73,000,000	(143,000,000)
Other changes	(19,000,000)	(17,000,000)
Sale of MSRs	0	0
Balance, as of March 31	433,000,000	367,000,000
MSR fees
Servicing fees	31,000,000	39,000,000
Late fees	1,000,000	2,000,000
Ancillary fees	0	0
Total MSR fees	32,000,000	41,000,000
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		1,600,000,000
Securities transferred to re-securitization entities	13,100,000,000	$ 7,400,000,000
Market value of retained interest related to re-securitization transaction	335,000,000.0		916,000,000.0
Original fair value of re-securitizations deals in which the entity holds a retained interest	$ 76,200,000,000		$ 83,600,000,000

No definition available.

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- Definition

Represents the fair value of capitalized mortgage servicing rights.

+ References

No definition available.

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- Definition

Represents the fair value of re-securitizations deals in which entity holds retained interest.

+ References

No definition available.

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- Definition

This element represents the amount of market value of interest owned by the entity in private-label re-securitization entities, for current period.

+ References

No definition available.

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Represents the amount of original fair value of re-securitizations deals in which the entity holds a retained interest.

+ References

No definition available.

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- Definition

Re-securitizations [Abstract]

+ References

No definition available.

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Represents the amount of securities transferred to re-securitization entities.

+ References

No definition available.

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- Definition

All amounts that are due to the servicer of a financial asset, excluding contractually specified servicing fees and late fees.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=116651436&loc=d3e122596-111746

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- Definition

All amounts that, per contract, are due to the servicer in exchange for servicing the financial asset and would no longer be received by a servicer if the beneficial owners of the serviced assets (or their trustees or agents) were to exercise their actual or potential authority under the contract to shift the servicing to another servicer. Depending on the servicing contract, those fees may include some or all of the difference between the interest rate collected on the asset being serviced and the rate to be paid to the beneficial owners of the asset.

+ References

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No definition available.

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- Definition

Income from mortgage banking activities (fees and commissions) and servicing real estate mortgages, credit cards, and other financial assets held by others net of any related impairment of capitalized service costs. Also includes any premiums received in lieu of regular servicing fees on such loans only as earned over the life of the loans.

+ References

No definition available.

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- Definition

All amounts that are due to the servicer of a financial asset as a result of the debt holder not meeting the monthly payment terms.

+ References

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- Definition

Amount of transferred financial assets in which the transferor has continuing involvement with the assets underlying the transaction that continue to be recognized in the statement of financial position. Includes, but is not limited to, servicing, recourse, and restrictions on transferor's interests in transferred financial assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=121570589&loc=d3e107314-111719

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- Definition

The value of new servicing assets, subsequently measured at fair value, acquired or created during the current period through purchases or from transfers of financial assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 3
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=116651436&loc=d3e122625-111746

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- Definition

Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 45
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122501-111745

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 45
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-URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122492-111745

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

Amount of increase (decrease) in fair value from changes in the inputs, assumptions, or model used to calculate the fair value of the contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 3
-Subparagraph (a)(4)(i)
-URI http://asc.fasb.org/extlink&oid=116651436&loc=d3e122625-111746

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- Definition

Decrease in servicing assets subsequently measured at fair value resulting from conveyance of servicing rights to unrelated parties.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=116651436&loc=d3e122625-111746

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Amount of increase (decrease) in fair value from changes classified as other for a contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 50
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