Reverse Mortgage Interests, Net - Schedule of Reverse Mortgage Interest (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Mortgage Servicing Rights [Line Items]
Participating interests in HECM mortgage-backed securities (“HMBS”), net of $36 and $58 premium, respectively	$ 5,293	$ 5,664
Other interests securitized, net of $112 and $100 discount, respectively	950	1,064
Unsecuritized interests, net of $95 and $122 discount, respectively	1,254	1,219
Reserves	(8)	(13)
Total reverse mortgage interests, net	7,489	7,934
Other interests securitized, discount	112	100
Unsecuritized interests, discount	95	122
Mortgage-backed debt
Mortgage Servicing Rights [Line Items]
Debt premium	$ 36	$ 58