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CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (Parenthetical) - USD ($) $ in Millions | 3 Months Ended
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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

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