Reverse Mortgage Interests, Net - Schedule of Reverse Mortgage Interest (Details) - USD ($) $ in Millions	Sep. 30, 2018	Jul. 31, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Mortgage Servicing Rights [Line Items]
Participating interests in HECM mortgage-backed securities, net of $55 and $0 premium, respectively	$ 6,074
Other interests securitized, net of $117 and $0 discount, respectively	1,003
Unsecuritized interests, net of $151 and $89 discount, respectively	1,810
Reserves	(1)	$ 0
Total reverse mortgage interests, net	8,886
Other interests securitized, discount	117	117
Unsecuritized interests, discount	151	161
Predecessor
Mortgage Servicing Rights [Line Items]
Participating interests in HECM mortgage-backed securities, net of $55 and $0 premium, respectively				$ 7,107
Other interests securitized, net of $117 and $0 discount, respectively				912
Unsecuritized interests, net of $151 and $89 discount, respectively				2,080
Reserves		$ (129)	$ (117)	(115)	$ (88)	$ (149)	$ (131)
Total reverse mortgage interests, net				9,984
Debt premium				62
Other interests securitized, discount				0
Unsecuritized interests, discount				89
Mortgage-backed debt
Mortgage Servicing Rights [Line Items]
Debt premium	$ 55
Mortgage-backed debt | Predecessor
Mortgage Servicing Rights [Line Items]
Debt premium				$ 0