Reverse Mortgage Interests, Net - Results (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Jul. 31, 2018
Debt Instrument [Line Items]
Participating interests in HECM mortgage-backed securities, including $10 and $58 purchase premium, respectively	$ 4,292	$ 5,664
Other interests securitized, net of $56 and $100 purchase discount, respectively	938	1,064
Unsecuritized interests, net of $68 and $122 purchase discount, respectively	1,052	1,219
Reserves	(3)	(13)
Total reverse mortgage interests, net	6,279	7,934
Other interests securitized, purchase discounts	56	100	$ 117
Unsecuritized interests, purchase discount	68	122	$ 173
Mortgage-backed debt
Debt Instrument [Line Items]
Unamortized premium	$ 10	$ 58