Investments AFS - Unrealized Loss Position Table (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
AFS - Fair Value - Less than 12 Months	$ 265,497	$ 5,465,767
AFS - Unrealized Losses - Less than 12 months	(377)	(18,023)
AFS - Fair Value - 12 months or longer	2,775,187	1,452,398
AFS - Unrealized Losses - 12 months or longer	(5,177)	(6,400)
AFS - Fair Value - Total in Continuous Loss Position	3,040,684	6,918,165
AFS - Unrealized Losses - Total in Continuous Loss Position	(5,554)	(24,423)
U.S. obligations single-family MBS
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
AFS - Fair Value - Less than 12 Months	0	492,038
AFS - Unrealized Losses - Less than 12 months	0	(1,022)
AFS - Fair Value - 12 months or longer	56,485	46,104
AFS - Unrealized Losses - 12 months or longer	(133)	(276)
AFS - Fair Value - Total in Continuous Loss Position	56,485	538,142
AFS - Unrealized Losses - Total in Continuous Loss Position	(133)	(1,298)
Private label MBS [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
AFS - Fair Value - Less than 12 Months	1,799	0
AFS - Unrealized Losses - Less than 12 months	(22)	0
AFS - Fair Value - 12 months or longer	2,611	2,979
AFS - Unrealized Losses - 12 months or longer	(318)	(182)
AFS - Fair Value - Total in Continuous Loss Position	4,410	2,979
AFS - Unrealized Losses - Total in Continuous Loss Position	(340)	(182)
MBS [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
AFS - Fair Value - Less than 12 Months	265,497	5,465,767
AFS - Unrealized Losses - Less than 12 months	(377)	(18,023)
AFS - Fair Value - 12 months or longer	2,775,187	1,452,398
AFS - Unrealized Losses - 12 months or longer	(5,177)	(6,400)
AFS - Fair Value - Total in Continuous Loss Position	3,040,684	6,918,165
AFS - Unrealized Losses - Total in Continuous Loss Position	(5,554)	(24,423)
Single Family [Member] \| GSE MBS [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
AFS - Fair Value - Less than 12 Months	49,120	2,458,728
AFS - Unrealized Losses - Less than 12 months	(86)	(6,318)
AFS - Fair Value - 12 months or longer	228,764	221,806
AFS - Unrealized Losses - 12 months or longer	(276)	(1,097)
AFS - Fair Value - Total in Continuous Loss Position	277,884	2,680,534
AFS - Unrealized Losses - Total in Continuous Loss Position	(362)	(7,415)
Multifamily [Member] \| GSE MBS [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
AFS - Fair Value - Less than 12 Months	214,578	2,515,001
AFS - Unrealized Losses - Less than 12 months	(269)	(10,683)
AFS - Fair Value - 12 months or longer	2,487,327	1,181,509
AFS - Unrealized Losses - 12 months or longer	(4,450)	(4,845)
AFS - Fair Value - Total in Continuous Loss Position	2,701,905	3,696,510
AFS - Unrealized Losses - Total in Continuous Loss Position	$ (4,719)	$ (15,528)

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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