Investments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013 security	Sep. 30, 2012	Sep. 30, 2013 security	Sep. 30, 2012	Dec. 31, 2012 security
Investments [Abstract]
Gross gains on investments	$ 7.1	$ 1.1	$ 9.9	$ 2.6
Gross losses on investments	0.1	0.1	0.2	0.5
Proceeds from sale of investment securities	$ 12.5	$ 3.5	$ 30.2	$ 9.7
Number of debt security positions	75		75		56