Reverse Mortgage Interests, Net - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounting standards update			us-gaap:AccountingStandardsUpdate201613Member		us-gaap:AccountingStandardsUpdate201613Member
Interest earned on HECM loans			$ 158,000,000	$ 241,000,000
Unsecuritized HECM
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest earned on HECM loans	$ 41,000,000	$ 74,000,000
Participating Interests in HMBS
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized			134,000,000	211,000,000
Government National Mortgage Association (GNMA) Insured Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized			0	61,000,000
Trust 2020-1
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized			516,000,000
2018-02 and 2018-03
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized			337,000,000
Trust 2019-1
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized				398,000,000
Trust 2017-2
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB called				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			912,000,000	2,132,000,000
Repurchase of HECM loans funded by prior servicer			244,000,000	561,000,000
Housing and urban development, home equity conversion mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unsecuritized interests			$ 630,000,000	$ 1,458,000,000