Investment Securities (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011 securities	Dec. 31, 2010	Dec. 31, 2009
Schedule of Investments [Line Items]
Proceeds from sales of mortgage-backed securities	$ 759,700,000	$ 1,040,000,000	$ 2,440,000,000
Proceeds from repayments of mortgage-backed securities	108,400,000	308,200,000	313,200,000
Proceeds from sales and repayments of other investment securities	525,000,000	65,100,000	51,700,000
Proceeds from maturity and calls of investment securities	435,000,000	2,880,000,000	1,430,000,000
Gains realized on sales and calls of investment securities	21,100,000	19,300,000	56,500,000
Realized losses on sales and calls of investment securities		67,000	9,000
Percentage of fair value securities, temporarily impaired	18.70%
Unrealized losses for securities with unrealized losses for less than twelve months, percentage of historical cost	5.40%
Securities with unrealized losses for twelve months or more, percentage of historical cost	9.20%
Number of issues of securities had unrealized losses for 12 months or longer	28
Number of issues of securities with unrealized losses of less than 12 months	30
Pledged investment securities at carrying value	1,680,000,000	1,800,000,000
Non-Agency Issues Rated Below Investment Grade [Member]
Schedule of Investments [Line Items]
Par amount of securities	430,000
Unrealized loss on securities	182,000
Other Issue [Member]
Schedule of Investments [Line Items]
Par amount of securities	7,000,000
Unrealized loss on securities	428,000
Corporate Bond Rated Below Investment Grade [Member]
Schedule of Investments [Line Items]
Par amount of securities	$ 5,000,000