Investing Activities - Sources of Net Investment Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Investments, Debt and Equity Securities [Abstract]
Debt securities	$ 31.9	$ 29.8
Policy loans	0.7	0.8
Limited partnerships and other investments	0.7	0.1
Fair value investments	0.3	0.3
Total investment income	33.6	31.0
Less: Investment expenses	0.6	0.4
Net investment income	$ 33.0	$ 30.6