Investment Securities (Narrative) (Details) (USD $)	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Proceeds from repayment and sale of mortgage-backed securities available-for-sale	$ 470,400,000	$ 680,900,000
Proceeds from repayments of mortgage-backed securities	60,900,000	117,900,000
Proceeds from sales and repayments of other investment securities	367,500,000	59,500,000
Proceeds from maturity and calls of investment securities	275,000,000	1,500,000,000
Gains realized on sales and calls of investment securities	11,400,000	8,700,000
Realized losses on sales and calls of investment securities	0	67,000
Percentage of fair value securities, temporarily impaired	30.70%
Unrealized losses for securities with unrealized losses for less than twelve months	1.70%
Securities with unrealized losses for twelve months or more	4.60%
Number of securities, temporarily impaired, below investment grade	2
Number of issues of securities had unrealized losses for 12 months for longer	11
Number of issues of securities with unrealized losses of less than 12 months	132
Impairment loss recognized	0
Pledged investment securities	1,470,000,000
Investment securities at carrying value			1,800,000,000
Securities purchased under agreements to resell	255,000,000		110,000,000
Rate of security purchased under agreement to resell	0.07%
Maturity date of security under resell agreement	July 18, 2011
B [Member] | B2 [Member]
Par amount of loan securities below investment grade	$ 8,300,000