Investments (Net Investment Income Summarized By Investment Type) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Investment income	$ 165.4	$ 152.8	$ 487.7	$ 473.5
Investment expenses	(5.6)	(5.5)	(16.8)	(16.6)
Net investment income	159.8	147.3	470.9	456.9
Total Fixed Maturity Securities [Member]
Investment income	80.7	72.4	242.5	240.1
Bonds [Member]
Investment income	77.8	79.2	235.2	243.1
S and P Five Hundred Index Options [Member]
Investment income	2.9	(6.8)	7.3	(3.0)
Net investment income	2.9	(6.8)	7.3	(3.0)
Commercial Mortgage Loans [Member]
Investment income	87.2	79.6	248.3	229.9
Total Real Estate [Member]
Investment income	0	0.1	0.1	0.8
Other Investment Classification [Member]
Investment income	$ (2.5)	$ 0.7	$ (3.2)	$ 2.7