Capital (Mandatorily Redeemable Capital Stock) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012 Institutions	Sep. 30, 2011	Sep. 30, 2012 Institutions		Sep. 30, 2011		Dec. 31, 2011
Capital [Abstract]
Common Stock, par value	$ 100		$ 100				$ 100
Dividends on mandatorily redeemable capital stock	$ 205	$ 0	$ 319		$ 0
Mandatorily Redeemable Capital Stock [Roll Forward]
Balance, beginning of the period			45,673		34,215
Due to withdrawals (includes mergers)			183,483		19,821
Withdrawals			0		(30)
Other redemptions			(41,028)	[1]	(5,929)	[1]
Balance, end of the period	$ 188,128	$ 48,077	$ 188,128		$ 48,077
Financial Instruments Subject to Mandatory Redemption, Number of Institutions	13		13
Financial Instruments Subject to Mandatory Redemption, Number of Institutions Assumed by FDIC	2		2
Financial Instruments Subject to Mandatory Redemption, Number of Institutions Voluntarily Dissolved	1		1
Financial Instruments Subject to Mandatory Redemption, Number of Nonmember Institutions	8		8
Financial Instruments Subject to Mandatory Redemption, Number of Institutions Ineligible for Membership	1		1
Financial Instruments Subject to Mandatory Redemption, Number of Institutions Voluntarily Withdrawn	1		1

[1] Reflects the impact on mandatorily redeemable capital stock related to partial excess capital stock repurchases.