CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Statement of Comprehensive Income [Abstract]
Net Income	$ 1,283.8	$ 1,407.2	$ 981.0
Other Comprehensive Income (Loss)
Change in Net Unrealized Gain (Loss) on Securities (net of tax expense (benefit) of $300.6; $(1,890.8); $(346.9))	1,109.3	(7,042.8)	(1,301.4)
Change in the Effect of Discount Rate Assumptions on the Liability for Future Policy Benefits, Net of Reinsurance (net of tax expense (benefit) of $(256.5); $2,385.1; $622.8)	(962.3)	8,884.6	2,361.8
Change in Net Loss on Hedges (net of tax benefit of $17.0; $19.2; $9.8)	(64.1)	(71.4)	(36.0)
Change in Foreign Currency Translation Adjustment (net of tax expense (benefit) of $0.9; $(0.1); $4.2)	69.0	(116.0)	(12.8)
Change in Unrecognized Pension and Postretirement Benefit Costs (net of tax expense (benefit) of $(2.7); $18.9; $42.1)	11.6	(61.9)	(134.0)
Total Other Comprehensive Income	140.3	1,716.3	1,145.6
Comprehensive Income	$ 1,424.1	$ 3,123.5	$ 2,126.6