Commitments and Contingencies (Details) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011	Sep. 30, 2012		Sep. 30, 2011	Dec. 31, 2011
Loss Contingencies [Line Items]
Standby Letters Of Credit, Final Expiration				2017
Other liabilities	$ 145,172,000			$ 145,172,000			$ 70,420,000
Assets Pledged as Collateral	759,400,000			759,400,000			886,700,000
Cash Collateral Held	430,600,000			430,600,000			542,000,000
Security Owned and Pledged as Collateral, Fair Value	328,800,000			328,800,000			344,700,000
Provision (benefit) for derivative counterparty credit losses	0		(1,850,000)	0		(1,850,000)
Standby Letters of Credit [Member]
Loss Contingencies [Line Items]
Expire Within One Year	6,577,252,000			6,577,252,000
Expire After One Year	122,657,000			122,657,000
Off-balance sheet commitments	6,699,909,000			6,699,909,000			6,702,082,000	[1]
Other liabilities	1,700,000			1,700,000			800,000
Standby Letters of Credit Issuance Commitments [Member]
Loss Contingencies [Line Items]
Off-balance sheet commitments	148,200,000			148,200,000			126,300,000
Loan Origination Commitments [Member]
Loss Contingencies [Line Items]
Expire Within One Year	988,575,000			988,575,000
Expire After One Year	10,000,000			10,000,000
Off-balance sheet commitments	998,575,000			998,575,000			553,134,000
Loan Purchase or Fund Commitments [Member]
Loss Contingencies [Line Items]
Expire Within One Year	28,813,000			28,813,000
Expire After One Year	0			0
Off-balance sheet commitments	28,813,000			28,813,000			13,984,000
Consolidated Obligation Bonds [Member]
Loss Contingencies [Line Items]
Expire Within One Year	5,130,000,000			5,130,000,000
Expire After One Year	0			0
Off-balance sheet commitments	5,130,000,000	[2]		5,130,000,000	[2]		55,000,000	[2]
Interest Rate Swap [Member] | Consolidated Obligation Bonds [Member]
Loss Contingencies [Line Items]
Off-balance sheet commitments	5,100,000,000			5,100,000,000			55,000,000
Minimum [Member]
Loss Contingencies [Line Items]
Standby Letters Of Credit, Original Terms				less than 1 month
Maximum [Member]
Loss Contingencies [Line Items]
Standby Letters Of Credit, Original Terms				5 years
Period for Advance Commitments				2 years
Period of Delivery Commitments				45 days
Open RepoPlus Advance Product [Member]
Loss Contingencies [Line Items]
Line of Credit Facility, Amount Outstanding	$ 6,600,000,000			$ 6,600,000,000			$ 7,300,000,000

[1] Includes approved requests to issue future standby letters of credit of $148.2 million and $126.3 million at September 30, 2012 and December 31, 2011, respectively.

[2] Includes $5.1 billion and $55.0 million of consolidated obligation bonds which were hedged with associated interest rate swaps at September 30, 2012 and December 31, 2011, respectively