Reverse Mortgage Interests, Net - Schedule of Reverse Mortgage Interest (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Participating interests in HECM mortgage-backed securities (“HMBS”), net of $16 and $10 purchase discount and premium, respectively	$ 4,027	$ 4,292
Other interests securitized, net of $44 and $56 purchase discount, respectively	851	938
Unsecuritized interests, net of $69 and $68 purchase discount, respectively	1,080	1,052
Reserves	(3)	(3)	$ (8)	$ (13)
Total reverse mortgage interests, net	5,955	6,279
Other interests securitized, purchase discount	44	56	112	100
Unsecuritized interests, purchase discount	69	68	$ 95	$ 122
Mortgage-backed debt
Accounts, Notes, Loans and Financing Receivable [Line Items]
Debt premium	$ 16	$ 10