Borrowed Funds (Details 1) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2011	Dec. 31, 2010
Repurchase Agreements [Member]
Average balances of borrowings and the maximum amount outstanding at any month end
Average balance outstanding during the period	$ 10,687,277	$ 15,034,110
Maximum balance outstanding at any month-end during the period	14,750,000	15,100,000
Weighted average rate during the period	4.27%	4.10%
FHLB Advances [Member]
Average balances of borrowings and the maximum amount outstanding at any month end
Average balance outstanding during the period	14,447,292	14,875,000
Maximum balance outstanding at any month-end during the period	$ 15,175,000	$ 14,875,000
Weighted average rate during the period	3.43%	4.04%