Reverse Mortgage Interests, Net - Reserves Roll Forward (Details) - USD ($) $ in Millions	1 Months Ended	2 Months Ended	3 Months Ended	7 Months Ended	9 Months Ended
	Jul. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Jul. 31, 2018	Sep. 30, 2017
Reverse Mortgage Interests Reserves [Roll Forward]
Balance - beginning of period		$ 0
Provision, net		1
Write-offs		0
Balance - end of period	$ 0	1		$ 0
Predecessor
Reverse Mortgage Interests Reserves [Roll Forward]
Balance - beginning of period	117	$ 129	$ 149	115	$ 131
Provision, net	12		22	32	44
Write-offs	0		83	18	87
Balance - end of period	$ 129		$ 88	$ 129	$ 88