Reverse Mortgage Interests, Net - Schedule of Reverse Mortgage Interest (Details) - USD ($) $ in Millions	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Mortgage Servicing Rights [Line Items]
Participating interests in HECM mortgage-backed securities (“HMBS”), net of $18 and $58 premium, respectively	$ 4,952		$ 5,664
Other interests securitized, net of $84 and $100 discount, respectively	1,023		1,064
Unsecuritized interests, net of $97 and $122 discount, respectively	1,143		1,219
Reserves	(8)	$ (8)	(13)	$ (117)	$ (134)	$ (115)
Total reverse mortgage interests, net	7,110		7,934
Other interests securitized, discount	84	112	100
Unsecuritized interests, discount	97	$ 95	122
Mortgage-backed debt
Mortgage Servicing Rights [Line Items]
Debt premium	$ 18		$ 58