Investing Activities - Sources of Net Investment Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013
Investments, Debt and Equity Securities [Abstract]
Debt securities	$ 37.8	[1]	$ 31.9	[1]
Limited partnerships and other investments	1.2		0.7
Policy loans	0.8		0.7
Fair value investments	0.8		0.3
Total investment income	40.6		33.6
Less: Investment expenses	0.6		0.6
Net investment income	$ 40.0		$ 33.0

[1] Includes net investment income on short-term investments.