Mortgage-Backed and Credit Risk Transfer Securities - Realized Gain (Loss) on Investments (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Gross realized gains on sale of investments	$ 24,721	$ 774	$ 2,208
Gross realized losses on sale of investments	(16,682)	(218,910)	(3,873)
Other-than-temporary impairment losses	(7,731)	(7,846)	(11,962)
Net unrealized gains (losses on trading securities)	0	(21)	22
Total gain (loss) on investments, net	624,466	(327,700)	(19,704)
MBS
Debt Securities, Available-for-sale [Line Items]
Net unrealized gains and losses on securities accounted for under the fair value option	626,104	(95,327)	(21,368)
GSE CRT
Debt Securities, Available-for-sale [Line Items]
Net unrealized gains and losses on securities accounted for under the fair value option	$ (1,946)	$ (6,370)	$ 15,269

Marketable Securities, Realized Gain, Excluding Other Than Temporary Impairments

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- Definition

Marketable Securities, Realized Loss, Excluding Other Than Temporary Impairments

+ References

No definition available.

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- Definition

Amount of unrealized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in net income (trading).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27357-111563

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The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 8A
-URI http://asc.fasb.org/extlink&oid=118954083&loc=SL6284422-111562

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Amount of unrealized and realized gain (loss) on investment in marketable security, including other-than-temporary impairment (OTTI).

+ References

No definition available.

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Amount of unrealized gain (loss) on investment in marketable security.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(7)(c))
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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