Advances (Portfolio by Year of Contractual Maturity) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Advances [Abstract]
Due in 1 year or less	$ 19,018,266	$ 14,129,734
Due after 1 year through 2 years	3,054,594	2,614,149
Due after 2 years through 3 years	4,666,804	3,071,155
Due after 3 years through 4 years	2,655,836	3,560,115
Due after 4 years through 5 years	4,744,309	2,193,086
Thereafter	2,503,450	3,744,103
Total par value	36,643,259	29,312,342
Discount on Affordable Housing Program Advances	(256)	(377)
Deferred Prepayment Fees on Advances	(14,527)	(16,653)
Hedging adjustments	1,110,145	1,309,489
Total book value	$ 37,738,621	$ 30,604,801
Due in 1 year or less, Weighted Average Interest Rate	0.85%	1.12%
Due after 1 year through 2 years, Weighted Average Interest Rate	1.94%	2.89%
Due after 2 years through 3 years, Weighted Average Interest Rate	2.88%	2.63%
Due after 3 years through 4 years, Weighted Average Interest Rate	4.79%	4.05%
Due after 4 years through 5 years, Weighted Average Interest Rate	1.51%	4.51%
Thereafter, Weighted Average Interest Rate	3.69%	4.20%
Total par value, Weighted Average Interest Rate	1.77%	2.44%