Reverse Mortgage Interests - Purchase Discount Rollforward (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Purchase discount, net, for reverse mortgage interests
Balance - beginning of period	$ (127)	$ (114)
Utilization of purchase discounts	35	10
Amortization, net of accretion	(1)	(25)
Balance - end of period	$ (93)	$ (129)