Other Comprehensive Income (Loss) and Accumulated Other Comprehensive Income - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Available for Sale Fixed Maturities with Portion of OTTI Recognized in Earnings	$ 2.1	$ 2.8
Other Net Unrealized Gains on Investments	241.2	324.8
Foreign Currency Translation Adjustments, Net of Income Taxes	(0.5)	0.2
Net Unrecognized Postretirement Benefit Costs, Net of Income Taxes	(93.8)	(105.1)
Accumulated Other Comprehensive Income	$ 149.0	$ 222.7