Investments AFS - Schedule of Reconciliation Table (Details) - USD ($)		Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost (1)	[1]	$ 10,010,280,000		$ 11,000,910,000
Allowance for Credit Losses (2)		(1,691,000)	$ (1,574,000)	0
OTTI Recognized in AOCI				0
Gross Unrealized Gains		149,987,000		121,282,000
Gross Unrealized Losses		(5,554,000)		(24,423,000)
AFS Securities		10,153,022,000		11,097,769,000
Available-for-Sale - Accrued Interest		19,300,000		24,400,000
GSE and TVA obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost (1)		1,607,356,000		1,508,264,000	[1]
Allowance for Credit Losses (2)		0
OTTI Recognized in AOCI		0
Gross Unrealized Gains		51,315,000		42,435,000
Gross Unrealized Losses		0		0
AFS Securities		1,658,671,000		1,550,699,000
State or local agency obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost (1)		234,097,000		238,496,000	[1]
Allowance for Credit Losses (2)		0
OTTI Recognized in AOCI				0
Gross Unrealized Gains		13,793,000		9,398,000
Gross Unrealized Losses		0		0
AFS Securities		247,890,000		247,894,000
Non-MBS [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost (1)		1,841,453,000		1,746,760,000
Allowance for Credit Losses (2)		0
OTTI Recognized in AOCI				0
Gross Unrealized Gains		65,108,000		51,833,000
Gross Unrealized Losses		0		0
AFS Securities		1,906,561,000		1,798,593,000
U.S. obligations single-family MBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost (1)		651,330,000		805,294,000	[1]
Allowance for Credit Losses (2)		0
OTTI Recognized in AOCI				0
Gross Unrealized Gains		7,490,000		3,590,000
Gross Unrealized Losses		(133,000)		(1,298,000)
AFS Securities		658,687,000		807,586,000
Private label MBS [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost (1)		232,906,000		274,624,000	[1]
Allowance for Credit Losses (2)		(1,691,000)
OTTI Recognized in AOCI				0
Gross Unrealized Gains		36,749,000		51,704,000
Gross Unrealized Losses		(340,000)		(182,000)
AFS Securities		267,624,000		326,146,000
MBS [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost (1)		8,168,827,000		9,254,150,000	[1]
Allowance for Credit Losses (2)	[2]	(1,691,000)
OTTI Recognized in AOCI				0
Gross Unrealized Gains		84,879,000		69,449,000
Gross Unrealized Losses		(5,554,000)		(24,423,000)
AFS Securities		8,246,461,000		9,299,176,000
Single Family [Member] | GSE MBS [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost (1)		3,675,908,000		4,053,700,000	[1]
OTTI Recognized in AOCI				0
Gross Unrealized Gains		28,991,000		9,574,000
Gross Unrealized Losses		(362,000)		(7,415,000)
AFS Securities		3,704,537,000		4,055,859,000
Multifamily [Member] | GSE MBS [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost (1)		3,608,683,000		4,120,532,000	[1]
OTTI Recognized in AOCI				0
Gross Unrealized Gains		11,649,000		4,581,000
Gross Unrealized Losses		(4,719,000)		(15,528,000)
AFS Securities		$ 3,615,613,000		$ 4,109,585,000

[1] Includes adjustments made to the cost basis of an investment for accretion, amortization, OTTI and/or fair value hedge accounting adjustments, and excludes accrued interest receivable of $19.3 million and $24.4 million at September 30, 2020 and December 31, 2019.

[2] Due to the adoption of ASU 2016-13, effective January 1, 2020, the Bank recorded an ACL for expected credit losses on AFS securities.