Reverse Mortgage Interests - Schedule of Revers Mortgage Interests, Net (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Aug. 01, 2018
Reverse Mortgage Interest [Abstract]
Participating interests in HECM mortgage-backed securities	$ 3,471	$ 4,282
Unsecuritized interests	964	1,117
Other interests securitized	945	994
Purchase discount, net	(127)	(114)	$ (164)	$ (256)
Total reverse mortgage interests, net	$ 5,253	$ 6,279