Reverse Mortgage Interests, Net - Schedule of Reverse Mortgage Interest (Details) - USD ($) $ in Millions	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Jul. 31, 2018
Mortgage Servicing Rights [Line Items]
Participating interests in HECM mortgage-backed securities (“HMBS”), including $14 and $58 purchase premium, respectively	$ 4,592		$ 5,664
Other interests securitized, net of $63 and $100 purchase discount, respectively	879		1,064
Unsecuritized interests, net of $75 and $122 purchase discount, respectively	1,204		1,219
Reserves	(13)	$ (8)	(13)	$ (1)	$ 0
Total reverse mortgage interests, net	6,662		7,934
Other interests securitized, discount	63	84	100	117	117
Unsecuritized interests, discount	75	$ 97	122	$ 151	$ 161
Mortgage-backed debt
Mortgage Servicing Rights [Line Items]
Debt premium	$ 14		$ 58