Schedule of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ (1,808.5)	$ (2,523.7)	$ (3,308.0)	$ (3,448.3)
Other Comprehensive Income (Loss) Before Reclassifications	529.4	749.7	121.7
Amounts Reclassified from AOCI	(185.8)	(34.6)	(18.6)
Total Other Comprehensive Income	715.2	784.3	140.3
Net Unrealized Loss on Securities
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(2,003.1)	(2,755.2)	(1,919.1)	(3,028.4)
Other Comprehensive Income (Loss) Before Reclassifications	655.9	(870.4)	1,069.3
Amounts Reclassified from AOCI	(96.2)	(34.3)	(40.0)
Total Other Comprehensive Income	752.1	(836.1)	1,109.3
Effect of Change in Discount Rate Assumptions on the LFPB
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	929.9	1,185.4	(648.4)	313.9
Other Comprehensive Income (Loss) Before Reclassifications	(255.5)	1,833.8	(962.3)
Amounts Reclassified from AOCI	0.0	0.0	0.0
Total Other Comprehensive Income	(255.5)	1,833.8	(962.3)
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(245.6)	(343.0)	(321.1)	(390.1)
Other Comprehensive Income (Loss) Before Reclassifications	97.4	(21.9)	69.0
Amounts Reclassified from AOCI	0.0	0.0	0.0
Total Other Comprehensive Income	97.4	(21.9)	69.0
Unrecognized Pension and Postretirement Benefit Costs
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(210.9)	(340.2)	(345.7)	(334.1)
Other Comprehensive Income (Loss) Before Reclassifications	35.7	(7.4)	(16.9)
Amounts Reclassified from AOCI	(93.6)	(12.9)	(5.3)
Total Other Comprehensive Income	129.3	5.5	(11.6)
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(278.8)	(270.7)	(73.7)	$ (9.6)
Other Comprehensive Income (Loss) Before Reclassifications	(4.1)	(184.4)	(37.4)
Amounts Reclassified from AOCI	4.0	12.6	26.7
Total Other Comprehensive Income	$ (8.1)	$ (197.0)	$ (64.1)