Advances (Advances by Year of Contractual Maturity or Next Call Date or Next Convertible Date) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Advances [Abstract]
Due in 1 year or less	$ 19,418,266	$ 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	2,103,450	3,744,103
Due in 1 year or less	21,350,266	17,478,985
Due after 1 year through 2 years	2,999,094	2,283,148
Due after 2 years through 3 years	4,556,304	2,922,405
Due after 3 years through 4 years	1,643,336	3,287,615
Due after 4 years through 5 years	4,097,309	1,044,586
Thereafter	1,996,950	2,295,603
Total par value	$ 36,643,259	$ 29,312,342