Schedule of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Jan. 01, 2021	Dec. 31, 2020
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ (3,308.0)	$ (3,448.3)	$ (5,164.6)	$ 4,166.0	$ (6,310.2)
Other Comprehensive Income (Loss) Before Reclassifications	121.7	1,721.9	1,219.3
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	(18.6)	5.6	73.7
Total Other Comprehensive Income	140.3	1,716.3	1,145.6
Net Unrealized Gain (Loss) on Securities
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(1,919.1)	(3,028.4)	4,014.4		5,315.8
Other Comprehensive Income (Loss) Before Reclassifications	1,069.3	(7,066.0)	(1,260.7)
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	(40.0)	(23.2)	40.7
Total Other Comprehensive Income	1,109.3	(7,042.8)	(1,301.4)
AOCI, Liability for Future Policy Benefit, Parent
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(648.4)	313.9	(8,570.7)	$ (10,932.5)
Other Comprehensive Income (Loss) Before Reclassifications	(962.3)	8,884.6	2,361.8
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	0.0	0.0	0.0
Total Other Comprehensive Income	(962.3)	8,884.6	2,361.8
Net Gain on Hedges
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(73.7)	(9.6)	61.8		97.8
Other Comprehensive Income (Loss) Before Reclassifications	(37.4)	(30.4)	14.7
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	26.7	41.0	50.7
Total Other Comprehensive Income	(64.1)	(71.4)	(36.0)
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(321.1)	(390.1)	(274.1)		(261.3)
Other Comprehensive Income (Loss) Before Reclassifications	69.0	(116.0)	(12.8)
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	0.0	0.0	0.0
Total Other Comprehensive Income	69.0	(116.0)	(12.8)
Unrecognized Pension and Postretirement Benefit Costs
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(345.7)	(334.1)	(396.0)		$ (530.0)
Other Comprehensive Income (Loss) Before Reclassifications	(16.9)	49.7	116.3
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	(5.3)	(12.2)	(17.7)
Total Other Comprehensive Income	$ (11.6)	$ 61.9	$ 134.0