Advances (Advance Redemption Terms) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Advances [Abstract]
Overdrawn Demand Deposit Accounts	$ 459	$ 0
Due in 1 year or less	6,008,461
Due after 1 year through 2 years	8,814,228
Due after 2 years through 3 years	7,797,061
Due after 3 years through 4 years	8,253,557
Due after 4 years through 5 years	9,096,719
Thereafter	18,028,567
Federal Home Loan Bank Advances At Par Value	57,999,052	53,620,778
Commitment Fees on Advances	(814)	(836)
Discount on Affordable Housing Program Advances	(18,076)	(19,308)
Federal Home Loan Bank Advances, Premium	3,684	3,774
Federal Home Loan Bank Advances, Discount	(15,899)	(13,578)
Hedging adjustments	314,367	353,131
Advances	58,282,314	53,943,961
Federal Home Loan Bank Advances, Maturities, Within One Year of Balance Sheet Date		12,178,645
Federal Home Loan Bank Advances, Maturities, Due After One To Two Years of Balance Sheet Date		5,020,941
Federal Home Loan Bank Advances, Maturities, Due After Two To Three Years of Balance Sheet Date		6,505,107
Federal Home Loan Bank Advances, Maturities, Due After Three To Four Years of Balance Sheet Date		6,171,525
Federal Home Loan Bank Advances, Maturities, Due After Four To Five Years of Balance Sheet Date		9,131,953
Federal Home Loan Bank Advances, Maturities, After Five Years of Balance Sheet Date		$ 14,612,607
Federal Home Loan Bank Advances, Weighted Average Interest Rate Of Amounts Overdrawn Demand Deposit	0.21%	0.00%
Federal Home Loan Bank Advances, Weighted Average Interest Rate of Amounts Maturing Within One Year of Balance Sheet Date	0.82%	0.48%
Federal Home Loan Bank Advances, Weighted Average Interest Rate of Amounts Maturing From One To Two Years of Balance Sheet Date	0.74%	1.07%
Federal Home Loan Bank Advances, Weighted Average Interest Rate of Amounts Maturing From Two To Three Years of Balance Sheet Date	0.55%	0.73%
Federal Home Loan Bank Advances, Weighted Average Interest Rate of Amounts Maturing From Three To Four Years of Balance Sheet Date	0.82%	0.86%
Federal Home Loan Bank Advances, Weighted Average Interest Rate of Amounts Maturing From Four To Five Years of Balance Sheet Date	0.84%	0.88%
Federal Home Loan Bank Advances, Weighted Average Interest Rate of Amounts Maturing After Five Years of Balance Sheet Date	0.62%	0.74%
Federal Home Loan Bank Advances, Weighted Average Interest Rate As Of Balance Sheet Date	0.71%	0.75%