- Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Unrealized Gains on Investments, Net of Income Taxes:
Available for Sale Fixed Maturities with Portion of OTTI Recognized in Earnings	$ 0.2	$ 0.1
Other Net Unrealized Gains on Investments	269.5	211.7
Foreign Currency Translation Adjustments, Net of Income Taxes	0.2	(0.9)
Net Unrecognized Postretirement Benefit Costs, Net of Income Taxes	(72.2)	(74.9)
Gain (Loss) on Cash Flow Hedges, Net of Income Taxes	(3.3)	1.0
Accumulated Other Comprehensive Income	$ 194.4	$ 137.0