Reverse Mortgage Interests, Net - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Mar. 31, 2019	Dec. 31, 2018	Aug. 01, 2018	Mar. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchase discount		$ 84		$ 84				$ 90	$ 89
Unsecuritized HECM
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest earned on HECM loans	$ 85	118	$ 167	237
Participating Interests in HMBS
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized	149	174	149	174
GNMA
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized	61		61
Trust 2019-1
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized	398		398
Trust 2017-2
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized	249		249
Trust 2018-3
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB sold			20
Trust 2018-1 and Trust 2018-2
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized		443		443
Trust 2016-2 and Trust 2016-3
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized		$ 284		284
Reverse Mortgage Interests, Unsecuritized | HECM
Accounts, Notes, Loans and Financing Receivable [Line Items]
Repurchase of HECM loans			1,457	2,109
Repurchase of HECM loans funded by prior servicer			371	$ 444
Other Interest Securitized and Unsecuritized Interests
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchase discount							$ 298
Receivables From Prior Servicers, Reverse Mortgage Interests
Accounts, Notes, Loans and Financing Receivable [Line Items]
Account receivables	13		13			$ 18
Mortgage-backed debt
Accounts, Notes, Loans and Financing Receivable [Line Items]
Debt premium	18		18			58
Mortgage-backed debt | Participating Interests in HMBS
Accounts, Notes, Loans and Financing Receivable [Line Items]
Debt premium	$ 18		$ 18		$ 36	$ 58	$ 42