CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Net Income	$ 793.0	$ 1,100.3	$ 523.4
Other Comprehensive Income (Loss)
Change in Net Unrealized Gain on Securities Before Adjustment (net of tax expense (benefit) of $250.2; $757.0; $(614.2))	983.0	2,870.9	(2,314.5)
Change in Adjustment to Deferred Acquisition Costs and Reserves for Future Policy and Contract Benefits, Net of Reinsurance (net of tax expense (benefit) of $(138.2); $(511.7); $371.7)	(531.2)	(1,942.6)	1,411.8
Change in Net Gain on Hedges (net of tax benefit of $23.8; $17.0; $8.2)	(90.0)	(62.8)	(31.7)
Change in Foreign Currency Translation Adjustment (net of tax expense (benefit) of $(4.3); $0.2; $(0.6))	20.3	23.6	(50.7)
Change in Unrecognized Pension and Postretirement Benefit Costs (net of tax expense (benefit) of $(34.8); $(9.3); $17.0)	45.2	37.6	(60.9)
Total Other Comprehensive Income (Loss)	336.9	851.5	(924.2)
Comprehensive Income	$ 1,129.9	$ 1,951.8	$ (400.8)