Investment Securities (Narrative) (Details) (USD $)	9 Months Ended		12 Months Ended
	Sep. 30, 2011 securities years	Sep. 30, 2010	Dec. 31, 2010
Schedule of Investments [Line Items]
Proceeds from sales of mortgage-backed securities	$ 759,700,000	$ 726,100,000
Proceeds from repayments of mortgage-backed securities	83,600,000	187,100,000
Proceeds from sales and repayments of other investment securities	503,600,000	65,100,000
Proceeds from maturity and calls of investment securities	467,700,000	2,300,000,000
Gains realized on sales and calls of investment securities	20,200,000	9,700,000
Realized losses on sales and calls of investment securities	0	67,000
Percentage of fair value securities, temporarily impaired	21.20%
Unrealized losses for securities with unrealized losses for less than twelve months	4.00%
Securities with unrealized losses for twelve months or more	8.70%
Number of issues of securities had unrealized losses for 12 months or longer	31
Number of issues of securities with unrealized losses of less than 12 months	34
Pledged investment securities at carrying value	1,600,000,000		1,800,000,000
Securities purchased under agreements to resell	80,000,000		110,000,000
Rate of security purchased under agreement to resell	0.07%
Maturity date of security under resell agreement	October, 2011
Non Agency Issues Rated Below Investment Grade [Member]
Schedule of Investments [Line Items]
Par amount of securities	433,000
Unrealized loss on securities	63,000
Other Issue [Member]
Schedule of Investments [Line Items]
Par amount of securities	7,255,000
Unrealized loss on securities	499,000
Corporate Bond Rated Below Investment Grade [Member]
Schedule of Investments [Line Items]
Par amount of securities	$ 5,000,000