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, 2017	Jul. 31, 2018	Sep. 30, 2017
Discount for Other Interest Securitized
Balance - beginning of period		$ (117)
Additions		0
Accretion		0
Balance - end of period	$ (117)	(117)		$ (117)
Discount for Unsecuritized Interests
Balance - beginning of period		(161)
Additions		0
Accretion		10
Balance - end of period	(161)	(151)		(161)
Mortgage-backed debt
Premium for Participating Interests in HMBS
Balance - end of period		55
Participating Interests in HMBS | Mortgage-backed debt
Premium for Participating Interests in HMBS
Balance - beginning of period		58
Additions		0
Amortization		(3)
Balance - end of period	58	55		58
Predecessor
Premium for Participating Interests in HMBS
Balance - beginning of period				62
Discount for Other Interest Securitized
Balance - beginning of period				0
Discount for Unsecuritized Interests
Balance - beginning of period				(89)
Purchase discounts for reverse mortgage interests
Balance - beginning of period	(84)	$ (82)	$ (43)	(89)	$ (43)
Additions	0		(75)	(7)	(75)
Accretion	2		22	14	22
Balance - end of period	$ (82)		$ (96)	(82)	$ (96)
Predecessor | Mortgage-backed debt
Premium for Participating Interests in HMBS
Balance - beginning of period				$ 0