CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (Parenthetical) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Change in Net Unrealized Gain on Securities Before Adjustment, Tax Expense (Benefit)	$ (169.5)	$ 206.5	$ (444.4)	$ 295.5
Change in Adjustment to Deferred Acquisition Costs and Reserves for Future Policy and Contract Benefits, Net of Reinsurance, Tax Expense (Benefit)	133.8	(162.6)	345.9	(229.9)
Change in Net Gain on Hedges, Tax Benefit	(1.6)	(6.3)	(3.9)	(12.3)
Change in Foreign Currency Translation Adjustment, Tax Benefit	0.3	0.0	0.3	0.0
Change in Unrecognized Pension and Postretirement Benefit Costs, Tax Expense	$ 2.0	$ 1.3	$ 2.7	$ 2.8