Loans and Allowance for Loan Losses (Narrative) (Details) (USD $)	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2011	Sep. 30, 2011	Dec. 31, 2010
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
Restructured loans performing under their modified terms	42,000,000	42,000,000	41,300,000
Aggregate restructured credit card loans held	22,100,000	22,100,000	18,800,000
Increase in personal real estate loans past due 30-89 days		47,800,000
Total average impaired loans	140,802,000	143,475,000	173,000,000
Number of loans largely contributing to the increase of business real estate loans		6
Consumer and personal real estate loans	350,000,000	350,000,000
Consumer and personal real estate loans, percentage of personal banking portfolio	9.00%	9.00%
Commitments to lend additional funds	9,100,000	9,100,000
Foreclosed real estate	23,800,000	23,800,000	12,000,000
Personal property acquired in repossession	4,100,000	4,100,000	10,400,000
Maximum [Member]
Real estate loans past due, maximum	12,000,000	12,000,000
Minimum [Member]
Real estate loans past due, minimum	$ 4,000,000	$ 4,000,000