CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Change in Net Unrealized Gain on Securities Before Adjustment, Tax Expense (Benefit)	$ (274.9)	$ 89.0
Change in Adjustment to Deferred Acquisition Costs and Reserves for Future Policy and Contract Benefits, Net of Reinsurance, Tax Expense (Benefit)	212.1	(67.3)
Change in Net Gain on Hedges, Tax Benefit	2.3	6.0
Change in Unrecognized Pension and Postretirement Benefit Costs, Tax Expense	$ 0.7	$ 1.5