Fair Value Measurements - Fair Value by Balance Sheet Line Item (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Financial assets
Reverse mortgage interests, net	$ 5,955.0	$ 6,279.0
Mortgage loans held for sale	3,922.0	4,077.0
Derivative financial instruments	294.0	153.0
Financial liabilities
Unsecured senior notes(1)	2,259.0	2,366.0
Advance facilities(1)	489.0	422.0
Warehouse facilities(1)	4,551.0	4,575.0
Mortgage servicing rights financing liability	43.0	37.0
Excess spread financing	1,242.0	1,311.0
Derivative financial instruments	223.0	15.0
Other nonrecourse debt	4,945.0	5,286.0
Participating interest financing(1)
Financial liabilities
Other nonrecourse debt	4,045.0	4,284.0
Trust 2019-2
Financial liabilities
Other nonrecourse debt	297.0	333.0
Trust 2019-1
Financial liabilities
Other nonrecourse debt	269.0	302.0
Trust 2018-3
Financial liabilities
Other nonrecourse debt	190.0	209.0
Trust 2018-2
Financial liabilities
Other nonrecourse debt	137.0	148.0
Recurring Fair Value Measurements
Financial assets
Cash and cash equivalents	579.0	329.0
Restricted cash	266.0	283.0
Advances and other receivables, net	685.0	988.0
Mortgage loans held for sale	3,922.0	4,077.0
Derivative financial instruments	294.0	153.0
Financial liabilities
Advance facilities(1)	489.0	422.0
Warehouse facilities(1)	4,551.0	4,575.0
Mortgage servicing rights financing liability	43.0	37.0
Excess spread financing	1,242.0	1,311.0
Derivative financial instruments	223.0	15.0
Recurring Fair Value Measurements \| Level 1
Financial assets
Cash and cash equivalents	579.0	329.0
Restricted cash	266.0	283.0
Advances and other receivables, net	0.0	0.0
Mortgage loans held for sale	0.0	0.0
Derivative financial instruments	0.0	0.0
Financial liabilities
Advance facilities(1)	0.0	0.0
Warehouse facilities(1)	0.0	0.0
Mortgage servicing rights financing liability	0.0	0.0
Excess spread financing	0.0	0.0
Derivative financial instruments	0.0	0.0
Recurring Fair Value Measurements \| Level 2
Financial assets
Cash and cash equivalents	0.0	0.0
Restricted cash	0.0	0.0
Advances and other receivables, net	0.0	0.0
Mortgage loans held for sale	3,922.0	4,077.0
Derivative financial instruments	294.0	153.0
Financial liabilities
Advance facilities(1)	489.0	422.0
Warehouse facilities(1)	4,551.0	4,575.0
Mortgage servicing rights financing liability	0.0	0.0
Excess spread financing	0.0	0.0
Derivative financial instruments	223.0	15.0
Recurring Fair Value Measurements \| Level 3
Financial assets
Cash and cash equivalents	0.0	0.0
Restricted cash	0.0	0.0
Advances and other receivables, net	685.0	988.0
Mortgage loans held for sale	0.0	0.0
Derivative financial instruments	0.0	0.0
Financial liabilities
Advance facilities(1)	0.0	0.0
Warehouse facilities(1)	0.0	0.0
Mortgage servicing rights financing liability	43.0	37.0
Excess spread financing	1,242.0	1,311.0
Derivative financial instruments	0.0	0.0
Nonrecurring Fair Value Measurements
Financial assets
Reverse mortgage interests, net	5,955.0	6,279.0
Financial liabilities
Unsecured senior notes(1)	2,259.0	2,366.0
Nonrecurring Fair Value Measurements \| Participating interest financing(1)
Financial liabilities
Other nonrecourse debt	4,056.0	4,299.0
Nonrecurring Fair Value Measurements \| Trust 2019-2
Financial liabilities
Other nonrecourse debt	295.0	331.0
Nonrecurring Fair Value Measurements \| Trust 2019-1
Financial liabilities
Other nonrecourse debt	268.0	300.0
Nonrecurring Fair Value Measurements \| Trust 2018-3
Financial liabilities
Other nonrecourse debt	189.0	208.0
Nonrecurring Fair Value Measurements \| Trust 2018-2
Financial liabilities
Other nonrecourse debt	137.0	148.0
Nonrecurring Fair Value Measurements \| Level 1
Financial assets
Reverse mortgage interests, net	0.0	0.0
Financial liabilities
Unsecured senior notes(1)	2,055.0	2,505.0
Nonrecurring Fair Value Measurements \| Level 1 \| Participating interest financing(1)
Financial liabilities
Other nonrecourse debt	0.0	0.0
Nonrecurring Fair Value Measurements \| Level 1 \| Trust 2019-2
Financial liabilities
Other nonrecourse debt	0.0	0.0
Nonrecurring Fair Value Measurements \| Level 1 \| Trust 2019-1
Financial liabilities
Other nonrecourse debt	0.0	0.0
Nonrecurring Fair Value Measurements \| Level 1 \| Trust 2018-3
Financial liabilities
Other nonrecourse debt	0.0	0.0
Nonrecurring Fair Value Measurements \| Level 1 \| Trust 2018-2
Financial liabilities
Other nonrecourse debt	0.0	0.0
Nonrecurring Fair Value Measurements \| Level 2
Financial assets
Reverse mortgage interests, net	0.0	0.0
Financial liabilities
Unsecured senior notes(1)	0.0	0.0
Nonrecurring Fair Value Measurements \| Level 2 \| Participating interest financing(1)
Financial liabilities
Other nonrecourse debt	0.0	0.0
Nonrecurring Fair Value Measurements \| Level 2 \| Trust 2019-2
Financial liabilities
Other nonrecourse debt	0.0	0.0
Nonrecurring Fair Value Measurements \| Level 2 \| Trust 2019-1
Financial liabilities
Other nonrecourse debt	0.0	0.0
Nonrecurring Fair Value Measurements \| Level 2 \| Trust 2018-3
Financial liabilities
Other nonrecourse debt	0.0	0.0
Nonrecurring Fair Value Measurements \| Level 2 \| Trust 2018-2
Financial liabilities
Other nonrecourse debt	0.0	0.0
Nonrecurring Fair Value Measurements \| Level 3
Financial assets
Reverse mortgage interests, net	6,015.0	6,318.0
Financial liabilities
Unsecured senior notes(1)	0.0	0.0
Nonrecurring Fair Value Measurements \| Level 3 \| Participating interest financing(1)
Financial liabilities
Other nonrecourse debt	4,056.0	4,299.0
Nonrecurring Fair Value Measurements \| Level 3 \| Trust 2019-2
Financial liabilities
Other nonrecourse debt	295.0	331.0
Nonrecurring Fair Value Measurements \| Level 3 \| Trust 2019-1
Financial liabilities
Other nonrecourse debt	268.0	300.0
Nonrecurring Fair Value Measurements \| Level 3 \| Trust 2018-3
Financial liabilities
Other nonrecourse debt	189.0	208.0
Nonrecurring Fair Value Measurements \| Level 3 \| Trust 2018-2
Financial liabilities
Other nonrecourse debt	$ 137.0	$ 148.0

Excess Spread Financing, Fair Value Disclosure

No definition available.

Name:	coop_ExcessSpreadFinancingFairValueDisclosure
Namespace Prefix:	coop_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Mortgage Servicing Rights Liability Resulting from Sale or Securitization of Servicer Advances, Rights not Accounted for as a Sale

+ References

No definition available.

+ Details

Name:	coop_MortgageServicingRightsLiabilityResultingfromSaleofServicerAdvancesRightsnotAccountedforasaSale
Namespace Prefix:	coop_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Reverse funded loan advances

+ References

No definition available.

+ Details

Name:	coop_ReverseFundedLoanAdvances
Namespace Prefix:	coop_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Services Advances, Net, Fair Value Disclosure

+ References

No definition available.

+ Details

Name:	coop_ServicesAdvancesNetFairValueDisclosure
Namespace Prefix:	coop_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

No definition available.

+ Details

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

- Definition

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226000-175313

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=118948506&loc=SL51823488-111719

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624163-113959

+ Details

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

- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13433-108611

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313

+ Details

Name:	us-gaap_DerivativeLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Fair value portion of mortgage loans held-for-sale.

+ References

No definition available.

+ Details

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

- Definition

Amount of debt for which creditor does not have general recourse to the debtor but rather has recourse only to the property used for collateral in the transaction or other specific property.

+ References

No definition available.

+ Details

Name:	us-gaap_NonRecourseDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value portion of notes payable.

+ References

+ Details

Name:	us-gaap_NotesPayableFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(2))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=98513485&loc=SL98516268-108586

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(1)(a))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3044-108585

+ Details

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

- Definition

Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

+ References

+ Details

Name:	us-gaap_SecuredDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of uncollateralized debt obligations (with maturities initially due after one year or beyond the operating cycle if longer).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

+ Details

Name:	us-gaap_UnsecuredDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_DebtInstrumentAxis=coop_ParticipatingInterestFinancingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=coop_A201902HECMSecuritizationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=coop_A201901HECMSecuritizationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=coop_A201803HECMSecuritizationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=coop_A201802HECMSecuritizationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsNonrecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: