Investing Activities - Sources of Net Investment Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Investments, Debt and Equity Securities [Abstract]
Debt securities [1]	$ 32.7	$ 31.2	$ 64.6	$ 61.0
Policy loans	0.8	0.8	1.5	1.6
Limited partnerships and other investments	0.6	0.9	1.3	1.0
Fair value investments	0.3	(0.1)	0.6	0.2
Total investment income	34.4	32.8	68.0	63.8
Less: Investment expenses	0.3	0.2	0.9	0.6
Net investment income	$ 34.1	$ 32.6	$ 67.1	$ 63.2