Fair value of the assets less the liabilities of a derivative or group of derivatives.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13433-108611

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Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5579245-113959

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Derivative Instruments and Hedging Activities Put and Call Options for TBAs (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Derivative, Notional Amount	$ 49,205,497,000	$ 36,528,169,000	$ 31,226,878,000
Derivative Financial Instruments, Liabilities [Member]
Derivative [Line Items]
Derivative, Notional Amount	34,862,360,000	5,403,265,000
Fair Value	$ (6,740,000)	(820,590,000)
Put and Call Options for TBAs [Member] \| Derivative Financial Instruments, Liabilities [Member]
Derivative [Line Items]
Derivative, Notional Amount		1,767,000,000
Fair Value		(25,296,000)
Put and Call Options for TBAs [Member] \| Long [Member]
Derivative [Line Items]
Derivative, Notional Amount		5,400,000,000
Put and Call Options for TBAs [Member] \| Short [Member]
Derivative [Line Items]
Derivative, Notional Amount		$ 7,200,000,000