Available-for-Sale Securities Securities with Unrealized Losses (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	$ 2,013,102	$ 967,090
Less than 12 Months, Unrealized Losses	(15,802)	(5,683)
12 Months or More, Fair Value	3,047,211	4,668,323
12 Months or More, Unrealized Losses	(66,552)	(148,144)
Total Fair Value	5,060,313	5,635,413
Total Unrealized Losses	(82,354)	(153,827)
HFA securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	12,229	11,118
Less than 12 Months, Unrealized Losses	(1,591)	(1,682)
12 Months or More, Fair Value	52,423	38,483
12 Months or More, Unrealized Losses	(3,077)	(4,217)
Total Fair Value	64,652	49,601
Total Unrealized Losses	(4,668)	(5,899)
Supranational institutions [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	0	0
Less than 12 Months, Unrealized Losses	0	0
12 Months or More, Fair Value	416,429	405,155
12 Months or More, Unrealized Losses	(12,925)	(14,067)
Total Fair Value	416,429	405,155
Total Unrealized Losses	(12,925)	(14,067)
U.S. government-owned corporations [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	0	0
Less than 12 Months, Unrealized Losses	0	0
12 Months or More, Fair Value	296,761	273,169
12 Months or More, Unrealized Losses	(26,431)	(24,560)
Total Fair Value	296,761	273,169
Total Unrealized Losses	(26,431)	(24,560)
GSEs [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	0	0
Less than 12 Months, Unrealized Losses	0	0
12 Months or More, Fair Value	123,786	115,627
12 Months or More, Unrealized Losses	(7,149)	(6,796)
Total Fair Value	123,786	115,627
Total Unrealized Losses	(7,149)	(6,796)
Other Than Mortgage-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	12,229	11,118
Less than 12 Months, Unrealized Losses	(1,591)	(1,682)
12 Months or More, Fair Value	889,399	832,434
12 Months or More, Unrealized Losses	(49,582)	(49,640)
Total Fair Value	901,628	843,552
Total Unrealized Losses	(51,173)	(51,322)
U.S. government-guaranteed - single-family MBS [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	10,885	0
Less than 12 Months, Unrealized Losses	(1)	0
12 Months or More, Fair Value	45,490	57,679
12 Months or More, Unrealized Losses	(2,288)	(3,437)
Total Fair Value	56,375	57,679
Total Unrealized Losses	(2,289)	(3,437)
U.S. government guaranteed - multifamily MBS [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	0	0
Less than 12 Months, Unrealized Losses	0	0
12 Months or More, Fair Value	282,617	361,134
12 Months or More, Unrealized Losses	(1,057)	(6,969)
Total Fair Value	282,617	361,134
Total Unrealized Losses	(1,057)	(6,969)
MBS [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	2,000,873	955,972
Less than 12 Months, Unrealized Losses	(14,211)	(4,001)
12 Months or More, Fair Value	2,157,812	3,835,889
12 Months or More, Unrealized Losses	(16,970)	(98,504)
Total Fair Value	4,158,685	4,791,861
Total Unrealized Losses	(31,181)	(102,505)
GSEs - single-family [Member] | GSEs – MBS [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	189,402	53,122
Less than 12 Months, Unrealized Losses	(968)	(388)
12 Months or More, Fair Value	1,423,927	3,417,076
12 Months or More, Unrealized Losses	(12,409)	(88,098)
Total Fair Value	1,613,329	3,470,198
Total Unrealized Losses	(13,377)	(88,486)
GSEs - multifamily [Member] | GSEs – MBS [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	1,800,586	902,850
Less than 12 Months, Unrealized Losses	(13,242)	(3,613)
12 Months or More, Fair Value	405,778	0
12 Months or More, Unrealized Losses	(1,216)	0
Total Fair Value	2,206,364	902,850
Total Unrealized Losses	$ (14,458)	$ (3,613)