Capital (Capital Requirements) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Capital [Abstract]
Risk-based capital - Required	$ 1,014,193	$ 1,062,070
Total capital-to-asset ratio - Required	4.00%	4.00%
Total regulatory capital - Required	2,405,620	2,079,771
Leverage ratio - Required	5.00%	5.00%
Leverage capital - Required	3,007,025	2,599,714
Risk-based capital - Actual	3,790,778	3,870,876
Total capital-to-asset ratio - Actual	6.30%	7.40%
Total regulatory capital - Actual	3,790,778	3,870,876
Leverage ratio - Actual	9.50%	11.20%
Leverage capital - Actual	$ 5,686,167	$ 5,806,313