Income Taxes - Comprehensive Income Tax Benefit and Expense (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Loss Carryforwards [Line Items]
Income Tax Expense	$ (2.9)	$ 11.8	$ 6.9	$ 4.3	$ 29.8	$ (0.8)	$ 1.9	$ 16.7	$ 20.1	$ 47.6	$ 99.9
Unrealized Depreciation (Appreciation) on Securities									62.8	(82.8)	129.1
Foreign Currency Translation Adjustments on Investments									0.5	0.4	(0.1)
Tax Effects from Postretirement Benefit Plans									(9.1)	34.7	(30.4)
Tax Effects from Long-term Equity-based Compensation included in Paid-in Capital									(1.0)	(1.0)	0.2
Comprehensive Income Tax Benefit (Expense)									(30.0)	97.4	2.8
Discontinued Operations [Member]
Operating Loss Carryforwards [Line Items]
Income Tax Expense									3.1	1.1	1.7
Continuing Operations [Member]
Operating Loss Carryforwards [Line Items]
Income Tax Expense									$ 20.1	$ 47.6	$ 99.9