Loans and Allowance for Loan Losses (Narrative) (Details) (USD $)	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2011	Jun. 30, 2011	Dec. 31, 2010
Loans and Allowance for Loan Losses
Loans pledged at the Federal Home Loan Bank as collateral for borrowings and letters of credit obtained to secure public deposits	$ 3,000,000,000	$ 3,000,000,000
Loans pledged at the Federal Reserve Bank as collateral for discount window borrowings	1,200,000,000	1,200,000,000
Loans outstanding for restructuring	48,500,000	48,500,000	41,300,000
Aggregate restructured credit card loans held	21,400,000	21,400,000	18,800,000
Total average impaired loans	143,883,000	144,833,000	173,000,000
Foreclosed real estate	23,600,000	23,600,000	12,000,000
Personal property acquired in repossession	4,500,000	4,500,000	10,400,000
Commitment to lend additional funds to borrowers with impaired loans	11,400,000	11,400,000
Commitment to lend additional funds to borrowers with restructured loans	$ 2,500,000	$ 2,500,000