Securitizations and Financings - Assets and Liabilities of Consolidated VIEs (Details) $ in Millions	3 Months Ended
Mar. 31, 2020 USD ($) special_purpose_entity	Dec. 31, 2019 USD ($)
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Number of SPEs \| special_purpose_entity	4
Assets - transfers accounted for as secured borrowings	$ 551	$ 606
Assets - reverse secured borrowings	4,921	5,272
Liabilities - transfers accounted for as secured borrowings	407	360
Liabilities - reverse secured borrowings	4,939	5,277
Purchase discount	60	46
Residential Mortgage \| Restricted cash
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Assets - transfers accounted for as secured borrowings	53	66
Assets - reverse secured borrowings	43	42
Residential Mortgage \| Reverse mortgage interests
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Assets - transfers accounted for as secured borrowings	0	0
Assets - reverse secured borrowings	4,878	5,230
Residential Mortgage \| Advances and other receivables, net
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Assets - transfers accounted for as secured borrowings	498	540
Assets - reverse secured borrowings	0	0
Residential Mortgage \| Advance facilities
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Liabilities - transfers accounted for as secured borrowings	407	359
Liabilities - reverse secured borrowings	0	0
Residential Mortgage \| Payables and other liabilities
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Liabilities - transfers accounted for as secured borrowings	0	1
Liabilities - reverse secured borrowings	1	1
Residential Mortgage \| Participating interest financing
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Liabilities - transfers accounted for as secured borrowings	0	0
Liabilities - reverse secured borrowings	4,045	4,284
Residential Mortgage \| Trust 2019-2 \| HECM Securitizations (HMBS)
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Liabilities - transfers accounted for as secured borrowings	0	0
Liabilities - reverse secured borrowings	297	333
Residential Mortgage \| Trust 2019-1 \| HECM Securitizations (HMBS)
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Liabilities - transfers accounted for as secured borrowings	0	0
Liabilities - reverse secured borrowings	269	302
Residential Mortgage \| Trust 2018-3 \| HECM Securitizations (HMBS)
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Liabilities - transfers accounted for as secured borrowings	0	0
Liabilities - reverse secured borrowings	190	209
Residential Mortgage \| Trust 2018-2 \| HECM Securitizations (HMBS)
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Liabilities - transfers accounted for as secured borrowings	0	0
Liabilities - reverse secured borrowings	$ 137	$ 148

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