CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Change in Net Unrealized Gain on Securities Before Adjustment, Tax Expense (Benefit)	$ 318.0	$ (892.5)	$ 725.8
Change in Adjustment to Deferred Acquisition Costs and Reserves for Future Policy and Contract Benefits, Net of Reinsurance, Tax Expense (Benefit)	(200.6)	856.6	(665.1)
Change in Net Gain on Cash Flow Hedges, Tax Benefit	25.4	4.3	2.0
Change in Foreign Currency Translation Adjustment, Tax Benefit	0.0	0.1	0.0
Change in Unrecognized Pension and Postretirement Benefit Costs, Tax Expense (Benefit)	$ (34.2)	$ 3.2	$ (92.4)