Schedule of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ (2,523.7)	$ (3,308.0)	$ (3,448.3)	$ (5,164.6)
Other Comprehensive Income (Loss) Before Reclassifications	749.7	121.7	1,721.9
Amounts Reclassified from AOCI	(34.6)	(18.6)	5.6
Total Other Comprehensive Income	784.3	140.3	1,716.3
Net Unrealized Gain (Loss) on Securities
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(2,755.2)	(1,919.1)	(3,028.4)	4,014.4
Other Comprehensive Income (Loss) Before Reclassifications	(870.4)	1,069.3	(7,066.0)
Amounts Reclassified from AOCI	(34.3)	(40.0)	(23.2)
Total Other Comprehensive Income	(836.1)	1,109.3	(7,042.8)
Effect of Change in Discount Rate Assumptions on the LFPB
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	1,185.4	(648.4)	313.9	(8,570.7)
Other Comprehensive Income (Loss) Before Reclassifications	1,833.8	(962.3)	8,884.6
Amounts Reclassified from AOCI	0.0	0.0	0.0
Total Other Comprehensive Income	1,833.8	(962.3)	8,884.6
Net Gain (Loss) on Derivatives
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(270.7)	(73.7)	(9.6)	61.8
Other Comprehensive Income (Loss) Before Reclassifications	(184.4)	(37.4)	(30.4)
Amounts Reclassified from AOCI	12.6	26.7	41.0
Total Other Comprehensive Income	(197.0)	(64.1)	(71.4)
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(343.0)	(321.1)	(390.1)	(274.1)
Other Comprehensive Income (Loss) Before Reclassifications	(21.9)	69.0	(116.0)
Amounts Reclassified from AOCI	0.0	0.0	0.0
Total Other Comprehensive Income	(21.9)	69.0	(116.0)
Unrecognized Pension and Postretirement Benefit Costs
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(340.2)	(345.7)	(334.1)	$ (396.0)
Other Comprehensive Income (Loss) Before Reclassifications	(7.4)	(16.9)	49.7
Amounts Reclassified from AOCI	(12.9)	(5.3)	(12.2)
Total Other Comprehensive Income	$ 5.5	$ (11.6)	$ 61.9