CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net Income	$ 1,100.3	$ 523.4	$ 994.2
Other Comprehensive Income (Loss)
Change in Net Unrealized Gain on Securities Before Adjustment (net of tax expense (benefit) of $757.0; $(614.2); $328.1)	2,870.9	(2,314.5)	721.7
Change in Adjustment to Deferred Acquisition Costs and Reserves for Future Policy and Contract Benefits, Net of Reinsurance (net of tax expense (benefit) of $(511.7); $371.7; $(245.0))	(1,942.6)	1,411.8	(554.5)
Change in Net Gain on Hedges (net of tax benefit of $17.0; $8.2; $24.4)	(62.8)	(31.7)	(45.2)
Change in Foreign Currency Translation Adjustment (net of tax expense (benefit) of $0.2; $(0.6); $—)	23.6	(50.7)	99.5
Change in Unrecognized Pension and Postretirement Benefit Costs (net of tax expense (benefit) of $(9.3); $17.0: $(8.3))	37.6	(60.9)	43.0
Total Other Comprehensive Income (Loss)	851.5	(924.2)	178.5
Comprehensive Income	$ 1,951.8	$ (400.8)	$ 1,172.7