Reverse Mortgage Interests - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Aug. 01, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchase discount, net	$ 127,000,000	$ 114,000,000	$ 164,000,000	$ 256,000,000
Interest earned on HECM loans	200,000,000	307,000,000
Participating Interests in HMBS
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized	173,000,000	265,000,000
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
Trust 2018-2 and Trust 2018-3
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized	337,000,000
Trust 2019-1 and Trust 2019-2
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized		751,000,000
Trust 2017-2 and Trust 2018-1
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized		476,000,000
Trust 2018-3
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid principal balance sold		20,000,000
Reverse Mortgage Interests, Unsecuritized | HECM
Accounts, Notes, Loans and Financing Receivable [Line Items]
Repurchase of HECM loans	1,153,000,000	2,333,000,000
Repurchase of HECM loans funded by prior servicer	306,000,000	616,000,000
Housing And Urban Development, Home Equity Conversion Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
HECM loans assigned to HUD	$ 771,000,000	$ 1,819,000,000