Fair Value Measurements - Reconciliation of Level 3 (Details) - Fair Value, Recurring - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Excess Spread Financing
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance - beginning of year	$ 1,311	$ 1,184
Total gains or losses included in earnings	(194)	(169)
Payments received from borrowers		0
Purchases, issuances, sales, repayments and settlements
Purchases	0	0
Issuances	24	542
Sales	0	0
Settlements and repayments	(207)	(246)
Transfers to mortgage loans held for sale		0
Transfers to real estate owned		0
Balance - end of year	934	1,311
Mortgage Servicing Rights Financing
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance - beginning of year	37	32
Total gains or losses included in earnings	(4)	5
Payments received from borrowers		0
Purchases, issuances, sales, repayments and settlements
Purchases	0	0
Issuances	0	0
Sales	0	0
Settlements and repayments	0	0
Transfers to mortgage loans held for sale		0
Transfers to real estate owned		0
Balance - end of year	33	37
Forward Mortgage Servicing Rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance - beginning of year	3,496	3,665
Total gains or losses included in earnings	(1,595)	(1,053)
Payments received from borrowers		0
Purchases, issuances, sales, repayments and settlements
Purchases	124	858
Issuances	687	434
Sales	(9)	(408)
Settlements and repayments	0	0
Transfers to mortgage loans held for sale		0
Transfers to real estate owned		0
Balance - end of year	2,703	3,496
IRLCs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance - beginning of year	135
Total gains or losses included in earnings	279
Purchases, issuances, sales, repayments and settlements
Purchases	0
Issuances	0
Sales	0
Settlements and repayments	0
Balance - end of year	414	135
LPCs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance - beginning of year	12
Total gains or losses included in earnings	26
Purchases, issuances, sales, repayments and settlements
Purchases	0
Issuances	0
Sales	0
Settlements and repayments	0
Balance - end of year	38	12
Mortgage Loans Held for Investment
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance - beginning of year	$ 0	119
Total gains or losses included in earnings		3
Payments received from borrowers		(11)
Purchases, issuances, sales, repayments and settlements
Purchases		0
Issuances		0
Sales		(94)
Settlements and repayments		0
Transfers to mortgage loans held for sale		(12)
Transfers to real estate owned		(5)
Balance - end of year		$ 0

Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements and Repayments

No definition available.

Name:	coop_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlementsAndRepayments
Namespace Prefix:	coop_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Fair Value, Measurement With Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfer To Mortgage Loans Held For Sale

+ References

No definition available.

+ Details

Name:	coop_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransferToMortgageLoansHeldForSale
Namespace Prefix:	coop_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Fair Value, Measurement With Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfer To Real Estate Owned

+ References

No definition available.

+ Details

Name:	coop_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransferToRealEstateOwned
Namespace Prefix:	coop_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements and Repayments

+ References

No definition available.

+ Details

Name:	coop_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlementsAndRepayments
Namespace Prefix:	coop_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Fair Value, Measurement With Unobservable Inputs Reconciliation, Recurring Basis, Liability, Transfer To Mortgage Loans Held For Sale

+ References

No definition available.

+ Details

Name:	coop_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityTransferToMortgageLoansHeldForSale
Namespace Prefix:	coop_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Fair Value, Measurement With Unobservable Inputs Reconciliation, Recurring Basis, Liability, Transfer To Real Estate Owned

+ References

No definition available.

+ Details

Name:	coop_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityTransferToRealEstateOwned
Namespace Prefix:	coop_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Payments From Borrowers

+ References

No definition available.

+ Details

Name:	coop_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetPaymentsFromBorrowers
Namespace Prefix:	coop_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Payments From Borrowers

+ References

No definition available.

+ Details

Name:	coop_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisLiabilityPaymentsFromBorrowers
Namespace Prefix:	coop_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- 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.

+ Details

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

- 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.

+ Details

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

- Definition

Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of issuances of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

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

- Definition

Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

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

- Definition

Amount of gain (loss) recognized in income from liability measured at fair value on recurring basis using unobservable input (level 3).

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of issuances of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of purchases of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

+ Details

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

- Definition

Amount of sales of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

+ Details

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

- Definition

Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

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

- Details

Name:	us-gaap_FairValueByLiabilityClassAxis=coop_ExcessSpreadFinancingMember
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_FairValueByLiabilityClassAxis=coop_MortgageServicingRightLiabilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=coop_MortgageServicingRightMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_InterestRateLockCommitmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_LoanPurchaseCommitmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=coop_MortgageLoansHeldForInvestmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: