Advances (Interest Rate Payment Terms) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Advances [Abstract]
Fixed rate – overnight	$ 165,890	$ 588,583
Fixed rate – term: Due in 1 year or less	18,802,376	13,487,574
Fixed rate – term: Thereafter	10,936,700	12,483,536
Total fixed rate	29,904,966	26,559,693
Variable rate: Due in 1 year or less	50,000	53,577
Variable rate: Thereafter	6,688,293	2,699,072
Total variable rate	6,738,293	2,752,649
Total par value	$ 36,643,259	$ 29,312,342