Mortgage Loans Held for Portfolio (Details) - USD ($) $ in Thousands		Jun. 30, 2017	Dec. 31, 2016
Mortgage Loans on Real Estate [Line Items]
Unpaid principal balance		$ 9,224,196	$ 8,925,673
Loans and Leases Receivable, Unamortized Premiums		215,517	211,058
Loans and Leases Receivable, Unamortized Discounts		(3,567)	(3,740)
Loans and Leases Receivable, Hedging Basis Adjustment	[1]	12,044	16,869
Loans and Leases Receivable, Gross, Consumer, Mortgage		9,448,190	9,149,860
Conventional Loan [Member]
Mortgage Loans on Real Estate [Line Items]
Unpaid principal balance		8,869,888	8,534,542
Federal Housing Administration Loan [Member]
Mortgage Loans on Real Estate [Line Items]
Unpaid principal balance		354,308	391,131
Single Family [Member] | Fixed rates medium-term single-family mortgages [Member]
Mortgage Loans on Real Estate [Line Items]
Unpaid principal balance	[2]	1,225,024	1,320,585
Single Family [Member] | Fixed rates Long-term single-family mortgages [Member]
Mortgage Loans on Real Estate [Line Items]
Unpaid principal balance		$ 7,999,172	$ 7,605,088

[1] Represents the unamortized balance of the mortgage purchase commitments' market values at the time of settlement. The market value of the commitment is included in the basis of the mortgage loan and amortized accordingly.

[2] Medium-term is defined as a term of 15 years or less.