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, 2019	Jul. 31, 2018	Sep. 30, 2019
Reverse Mortgage Interests Reserves [Roll Forward]
Balance - beginning of period		$ 0	$ 8		$ 13
Provision (release), net		1	5		7
Write-offs		0	0		(7)
Balance - end of period	$ 0	1	$ 13	$ 0	$ 13
Nationstar Mortgage Holdings Inc.
Reverse Mortgage Interests Reserves [Roll Forward]
Balance - beginning of period	117	$ 129		115
Provision (release), net	12			32
Write-offs	0			(18)
Balance - end of period	$ 129			$ 129