Reverse Mortgage Interests - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income on reverse mortgages	$ 40	$ 62
Participating Interests in HMBS
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized	33	52
Reverse mortgage interests, unsecuritized | HECM
Accounts, Notes, Loans and Financing Receivable [Line Items]
Repurchase of HECM loans	216	383
Repurchase of HECM loans funded by prior servicer	66	103
Housing and urban development, home equity conversion mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unsecuritized interests	$ 137	$ 266