Indebtedness - Summary of Other Non-Recourse Debt (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Other nonrecourse debt principal amount	$ 4,707	$ 5,286
Nonrecourse debt–legacy assets
Debt Instrument [Line Items]
Other nonrecourse debt principal amount	4,707	5,286
Unamortized debt issuance costs, premium and discount	8	10
Nonrecourse debt–legacy assets \| Participating interest financing
Debt Instrument [Line Items]
Collateral Amount	0
Other nonrecourse debt principal amount	3,875	4,284
Nonrecourse debt–legacy assets \| Trust 2019-2
Debt Instrument [Line Items]
Collateral Amount	287
Other nonrecourse debt principal amount	274	333
Nonrecourse debt–legacy assets \| Trust 2019-1
Debt Instrument [Line Items]
Collateral Amount	264
Other nonrecourse debt principal amount	244	302
Nonrecourse debt–legacy assets \| Trust 2018-3
Debt Instrument [Line Items]
Collateral Amount	200
Other nonrecourse debt principal amount	179	209
Nonrecourse debt–legacy assets \| Trust 2018-2
Debt Instrument [Line Items]
Collateral Amount	149
Other nonrecourse debt principal amount	127	148
Nonrecourse debt–legacy assets \| Other
Debt Instrument [Line Items]
Other nonrecourse debt principal amount	$ 4,699	$ 5,276

Amount of assets pledged to secure a debt instrument.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

+ Details

Name:	us-gaap_DebtInstrumentCollateralAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of unamortized debt discount (premium) and debt issuance costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28555-108399

+ Details

Name:	us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet
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

- Details

Name:	us-gaap_LongtermDebtTypeAxis=nsm_NonrecourseDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=nsm_A201902HECMSecuritizationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=nsm_A201901HECMSecuritizationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=nsm_A201803HECMSecuritizationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=nsm_A201802HECMSecuritizationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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