Reverse Mortgage Interests, Net - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Aug. 01, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized	$ 0
Unsecuritized HECM
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest earned on HECM loans	82,000,000
Participating Interests in HMBS
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized	82,000,000
GNMA
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized	61,000,000
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	740,000,000
Repurchase of HECM loans funded by prior servicer	188,000,000
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	16,000,000		$ 18,000,000
Mortgage-backed debt
Accounts, Notes, Loans and Financing Receivable [Line Items]
Debt premium	36,000,000		58,000,000
Mortgage-backed debt | Participating Interests in HMBS
Accounts, Notes, Loans and Financing Receivable [Line Items]
Debt premium	$ 36,000,000		$ 58,000,000	$ 42,000,000
Predecessor
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchase discount		$ (90,000,000)			$ (89,000,000)
Predecessor | Unsecuritized HECM
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest earned on HECM loans		119,000,000
Predecessor | Participating Interests in HMBS
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized		85,000,000
Predecessor | Trust 2018-1 and Trust 2018-2
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized		443,000,000
Predecessor | Trust 2016-2 and Trust 2016-3
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized		284,000,000
Predecessor | Reverse Mortgage Interests, Unsecuritized | HECM
Accounts, Notes, Loans and Financing Receivable [Line Items]
Repurchase of HECM loans		1,051,000,000
Repurchase of HECM loans funded by prior servicer		$ 229,000,000