Commitments and Contingencies (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Standby Letters of Credit [Member]
Loss Contingencies [Line Items]
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Expiring Within One Year	$ 11,391,637		$ 9,958,329
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Expiring After One Year	291,722		193,635
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Liability	11,683,359		10,151,964
Commitments for Standby Bond Purchases [Member]
Loss Contingencies [Line Items]
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Expiring Within One Year	173,595		313,055
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Expiring After One Year	189,170		66,760
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Liability	362,765		379,815
Loan Origination Commitments [Member]
Loss Contingencies [Line Items]
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Expiring Within One Year	14,000		0
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Expiring After One Year	0		0
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Liability	14,000		0
Commitments to Invest in Mortgage Loans [Member]
Loss Contingencies [Line Items]
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Expiring Within One Year	111,546		123,588
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Expiring After One Year	0		0
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Liability	111,546		123,588
Consolidated Obligation Bonds [Member]
Loss Contingencies [Line Items]
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Expiring Within One Year	3,375,000	[1]	110,000	[1]
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Expiring After One Year	0	[1]	0	[1]
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Liability	3,375,000	[1]	110,000	[1]
Discount Notes [Member]
Loss Contingencies [Line Items]
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Expiring Within One Year	7,833	[1]	750,000	[1]
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Expiring After One Year	0	[1]	0	[1]
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Liability	$ 7,833	[1]	$ 750,000	[1]

[1] Expiration is based on settlement period rather than underlying contractual maturity of Consolidated Obligations.