Residential Whole Loans (Narrative) (Details) - USD ($) $ in Billions	Sep. 30, 2018	Dec. 31, 2017
Receivables [Abstract]
Total residential whole loans	$ 3.9	$ 2.2

Loans, Including Fair Value Loans, Credit Impaired Loans and Other Loans at Carrying Value

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant