Reverse Mortgage Interests, Net - Purchase Discount Rollforward (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
Net Discount for Other Interest Securitized
Balance - beginning of period		$ (117)	$ (84)		$ (100)
Adjustments					(2)
Utilization of purchase discounts(2)			11		24
Accretion		0	9		22
Transfers			1		(7)
Balance - end of period	$ (117)	(117)	(63)	$ (117)	(63)
Net Discount for Unsecuritized Interests
Balance - beginning of period		(161)	(97)		(122)
Additions					(6)
Utilization of purchase discounts(2)			29		56
Accretion		10	(6)		3
Transfers			(1)		(6)
Balance - end of period	(161)	(151)	(75)	(161)	(75)
Purchase discounts for reverse mortgage interests
Balance - beginning of period					(42)
Balance - end of period			(49)		(49)
Mortgage-backed debt
Net Premium for Participating Interests in HMBS
Balance - beginning of period					58
Balance - end of period			14		14
Participating Interests in HMBS | Mortgage-backed debt
Net Premium for Participating Interests in HMBS
Balance - beginning of period		58	18		58
Adjustments					(16)
Utilization of purchase discounts(2)			0		0
Amortization		(3)	(4)		(41)
Transfers			0		13
Balance - end of period	58	55	$ 14	58	$ 14
Nationstar Mortgage Holdings Inc.
Purchase discounts for reverse mortgage interests
Balance - beginning of period	(84)	$ (82)		(89)
Additions	0			(7)
Accretion	2			14
Balance - end of period	$ (82)			$ (82)