Capital (Dividends and Retained Earnings) (Details) (USD $)	0 Months Ended			1 Months Ended	9 Months Ended
	Oct. 31, 2012	Jul. 31, 2012	Apr. 30, 2012	Feb. 28, 2012	Oct. 31, 2012	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Capital [Line Items]
Joint Capital Enhancement Agreement Percentage						20.00%
Retained Earnings (Accumulated Deficit)						$ 510,927,000		$ 435,340,000
Percent of Average Balance of Outstanding Consolidated Obligations Required per the Joint Capital Enhancement Agreement For Each Previous Quarter						1.00%
Retained Earnings, Unappropriated						490,763,000		430,774,000
Retained Earnings, Appropriated						20,164,000		4,566,000
Dividends, Per Share, Cash, Annualized Rate	0.43%	0.10%	0.10%	0.10%
Excess Capital						796,300,000
Repurchase/redemption of capital stock					477,000,000	436,079,000	538,824,000
Dividend Paid [Member]
Capital [Line Items]
Dividends, Per Share, Cash, Annualized Rate	0.43%
Repurchase of Equity [Member]
Capital [Line Items]
Repurchase/redemption of capital stock	300,000,000