SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Loan Delinquencies and Liquidation Losses (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Mortgage securitizations - Non-agency-sponsored
Variable Interest Entity
Securitized assets past due	$ 34,000.0	$ 18,300.0
Securitized assets liquidation losses	49.0	54.0
Mortgage securitizations - Non-agency-sponsored \| 90 days past due
Variable Interest Entity
Securitized assets past due	400.0	400.0
Mortgage-backed securities - Residential
Variable Interest Entity
Securitized assets past due	11,700.0	5,200.0
Securitized assets liquidation losses	49.0	54.0
Mortgage-backed securities - Residential \| 90 days past due
Variable Interest Entity
Securitized assets past due	400.0	400.0
Mortgage-backed securities - Commercial
Variable Interest Entity
Securitized assets past due	22,300.0	13,100.0
Securitized assets liquidation losses	0.0	0.0
Mortgage-backed securities - Commercial \| 90 days past due
Variable Interest Entity
Securitized assets past due	$ 0.0	$ 0.0

This is the principal amount of loans (across all types of loans) that are overdue in payment by a set number of days.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (e)(4)
-URI http://asc.fasb.org/extlink&oid=118948506&loc=d3e107314-111719

+ Details

Name:	us-gaap_DelinquentAmountAtEndOfPeriodOnLoansManagedAndSecuritized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of credit loss after recoveries for transferred financial assets that continue to be recognized in the statement of financial position.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (e)(5)
-URI http://asc.fasb.org/extlink&oid=118948506&loc=d3e107314-111719

+ Details

Name:	us-gaap_NetCreditLossOnLoansManagedOrSecuritizedOrAssetbackedFinancingArrangement
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_VariableInterestEntityLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablesPeriodPastDueAxis=us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ResidentialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CommercialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: