Advances (Narrative) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Advances [Line Items]
Federal Home Loan Bank, Advances, Interest Rate on Affordable Housing Program Subsidized Loans	0.00%
Callable Federal Home Loan Bank Advances	$ 9,805,376	$ 12,012,609
Putable Federal Home Loan Bank Advances	$ 2,469,250	$ 2,587,250
Percent Of Fixed Rate Advances Swapped To Adjustable Rate	33.00%	24.00%
Minimum [Member]
Advances [Line Items]
Federal Home Loan Bank Advances, Interest Rate	0.00%	0.00%
Maximum [Member]
Advances [Line Items]
Federal Home Loan Bank Advances, Interest Rate	9.20%	9.20%