Mortgage Servicing Rights and Related Liabilities - Fair Value Sensitivity Analysis (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Mortgage servicing rights
Excess Spread Financing - Hypothetical Sensitivities
10% Adverse Change	$ (175)	$ (165)
20% Adverse Change	(335)	(317)
Excess spread financing
Excess Spread Financing - Hypothetical Sensitivities
10% Adverse Change	47	46
20% Adverse Change	97	96
100 bps Adverse Change \| Mortgage servicing rights
Excess Spread Financing - Hypothetical Sensitivities
Discount Rate	(104)	(127)
100 bps Adverse Change \| Excess spread financing
Excess Spread Financing - Hypothetical Sensitivities
Discount Rate	38	46
200 bps Adverse Change \| Mortgage servicing rights
Excess Spread Financing - Hypothetical Sensitivities
Discount Rate	(201)	(245)
200 bps Adverse Change \| Excess spread financing
Excess Spread Financing - Hypothetical Sensitivities
Discount Rate	$ 78	$ 95

The hypothetical financial impact of a 10 percent adverse change of prepayment speed on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121570589&loc=d3e107314-111719

+ Details

Name:	us-gaap_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesImpactOf10PercentAdverseChangeInPrepaymentSpeed
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The hypothetical financial impact of a 20 percent adverse change of prepayment speed on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

+ References

+ Details

Name:	us-gaap_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesImpactOf20PercentAdverseChangeInPrepaymentSpeed
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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

- Definition

The hypothetical financial impact of a specified adverse percentage change in discount rate on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

+ References

+ Details

Name:	us-gaap_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesImpactOfOtherThan10Or20PercentAdverseChangeInDiscountRate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

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

- Details

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

- Details

Name:	nsm_ChangeInDiscountRateAxis=nsm_OneHundredBasisPointsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	nsm_ChangeInDiscountRateAxis=nsm_TwoHundredBasisPointsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: