Borrowed Funds (Details 1) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 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	$ 9,665,923	$ 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	4.33%	4.10%
FHLB Advances [Member]
Average balances of borrowings and the maximum amount outstanding at any month end
Average balance outstanding during the period	13,980,622	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	3.42%	4.04%