Reverse Mortgage Interests, Net - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Aug. 01, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair Value	$ 23		$ 22
Purchase discount	60		46
Unsecuritized HECM
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest earned on HECM loans	62	$ 82
Trust 2018-3
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB sold		20
Participating Interests in HMBS
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized	52	82
Government National Mortgage Association (GNMA) Insured Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized		61
Other Interest Securitized and Unsecuritized Interests
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchase discount				$ 298
Reverse Mortgage Interests, Unsecuritized | HECM
Accounts, Notes, Loans and Financing Receivable [Line Items]
Repurchase of HECM loans	383	740
Repurchase of HECM loans funded by prior servicer	103	188
Housing And Urban Development, Home Equity Conversion Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unsecuritized interests	266	$ 514
Mortgage-backed debt
Accounts, Notes, Loans and Financing Receivable [Line Items]
Debt premium	$ 16		$ 10
Mortgage-backed debt | Participating Interests in HMBS
Accounts, Notes, Loans and Financing Receivable [Line Items]
Debt premium				$ 42