Investment Securities (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011 Securities Lending Program [Member]	Dec. 31, 2010 Securities Lending Program [Member]
Percentage of collateral to fair value of investment securities on loan					102.00%
Fair value of securities on loan					$ 34.1	$ 54.0
Percentage of debt securities considered to be of investment-grade	95.00%		95.00%
Percentage of tax-exempt municipal securities classified as pre-refunded	13.00%		13.00%
Percentage of tax-exempt securities insured by bond insurers	25.00%		25.00%
Residential and commercial mortgage-backed securities, percentage of collateral consisting of prime loans	99.00%		99.00%
Other-than-temporary impairments	$ 0	$ 0	$ 0	$ 0