Reverse Mortgage Interests, Net - Narrative (Details) - USD ($)	1 Months Ended	2 Months Ended	3 Months Ended	7 Months Ended	9 Months Ended
	Jul. 31, 2018	Sep. 30, 2018	Sep. 30, 2019	Jul. 31, 2018	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Aug. 01, 2018	Jun. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized		$ 0
Purchase discount			$ 49,000,000		$ 49,000,000		$ 42,000,000
Unsecuritized HECM
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest earned on HECM loans		72,000,000	74,000,000		241,000,000
Participating Interests in HMBS
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized		44,000,000	211,000,000		211,000,000
GNMA
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized			61,000,000		61,000,000
Trust 2019-1
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized			398,000,000		398,000,000
Trust 2017-2
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized			249,000,000		249,000,000
Trust 2018-3
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB sold					20,000,000
Reverse Mortgage Interests, Unsecuritized | HECM
Accounts, Notes, Loans and Financing Receivable [Line Items]
Repurchase of HECM loans		608,000,000			2,132,000,000
Repurchase of HECM loans funded by prior servicer		138,000,000			561,000,000
HECM Loans, HUD
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unsecuritized interests		458,000,000			1,458,000,000
Other Interest Securitized and Unsecuritized Interests
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchase discount								$ 298,000,000
Receivables From Prior Servicers, Reverse Mortgage Interests
Accounts, Notes, Loans and Financing Receivable [Line Items]
Account receivables			8,000,000		8,000,000		18,000,000
Mortgage-backed debt
Accounts, Notes, Loans and Financing Receivable [Line Items]
Debt premium			14,000,000		14,000,000		58,000,000
Mortgage-backed debt | Participating Interests in HMBS
Accounts, Notes, Loans and Financing Receivable [Line Items]
Debt premium	$ 58,000,000	$ 55,000,000	$ 14,000,000	$ 58,000,000	$ 14,000,000	$ 18,000,000	$ 58,000,000	$ 42,000,000
Nationstar Mortgage Holdings Inc.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchase discount	82,000,000			82,000,000					$ 84,000,000	$ 89,000,000
Nationstar Mortgage Holdings Inc. | Unsecuritized HECM
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest earned on HECM loans	38,000,000			274,000,000
Nationstar Mortgage Holdings Inc. | Participating Interests in HMBS
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized	198,000,000			198,000,000
Nationstar Mortgage Holdings Inc. | Trust 2018-1 and Trust 2018-2
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized	760,000,000			760,000,000
Nationstar Mortgage Holdings Inc. | Trust 2016-2 and Trust 2016-3
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized	$ 284,000,000			284,000,000
Nationstar Mortgage Holdings Inc. | Reverse Mortgage Interests, Unsecuritized | HECM
Accounts, Notes, Loans and Financing Receivable [Line Items]
Repurchase of HECM loans				2,439,000,000
Repurchase of HECM loans funded by prior servicer				512,000,000
Nationstar Mortgage Holdings Inc. | HECM Loans, HUD
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unsecuritized interests				$ 1,712,000,000