Reverse Mortgage Interests, Net - Purchase Discount Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Net Discount for Other Interest Securitized
Balance - beginning of period	$ (112)		$ (100)
Adjustments			(2)
Utilization of purchase discounts	7		13
Accretion	28		13
Transfers	(7)		(8)
Balance - end of period	(84)		(84)
Net Discount for Unsecuritized Interests
Balance - beginning of period	(95)		(122)
Additions			(6)
Utilization of purchase discounts	5		27
Accretion	(9)		9
Transfers	2		(5)
Balance - end of period	(97)		(97)
Purchase discounts for reverse mortgage interests
Balance - beginning of period		$ (90)		$ (89)
Additions		0		(7)
Accretion		6		12
Balance - end of period		$ (84)		$ (84)
Mortgage-backed debt
Net Premium for Participating Interests in HMBS
Balance - beginning of period			58
Balance - end of period	18		18
Participating Interests in HMBS | Mortgage-backed debt
Net Premium for Participating Interests in HMBS
Balance - beginning of period	36		58
Adjustments			(16)
Utilization of purchase discounts	0		0
Amortization	(23)		(37)
Transfers	5		13
Balance - end of period	$ 18		$ 18