Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Accumulated Other Comprehensive Income (Loss)
Balance at Beginning of Period	$ (2,178.8)	$ (2,940.0)	$ (2,523.7)	$ (3,308.0)
Other Comprehensive Income (Loss) Before Reclassifications	110.5	86.4	297.8	443.2
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	27.6	7.4	185.2	18.6
Net Other Comprehensive Income	138.1	93.8	483.0	461.8
Balance at End of Period	(2,040.7)	(2,846.2)	(2,040.7)	(2,846.2)
Net Unrealized Loss on Securities
Accumulated Other Comprehensive Income (Loss)
Balance at Beginning of Period	(2,333.2)	(2,360.8)	(2,755.2)	(1,919.1)
Other Comprehensive Income (Loss) Before Reclassifications	53.6	(370.6)	319.2	(824.7)
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	25.9	7.6	182.3	20.0
Net Other Comprehensive Income	79.5	(363.0)	501.5	(804.7)
Balance at End of Period	(2,253.7)	(2,723.8)	(2,253.7)	(2,723.8)
Effect of Change in Discount Rate Assumptions on the LFPB
Accumulated Other Comprehensive Income (Loss)
Balance at Beginning of Period	1,019.1	225.3	1,185.4	(648.4)
Other Comprehensive Income (Loss) Before Reclassifications	39.8	487.0	(126.5)	1,360.7
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	0.0	0.0	0.0	0.0
Net Other Comprehensive Income	39.8	487.0	(126.5)	1,360.7
Balance at End of Period	1,058.9	712.3	1,058.9	712.3
Net Loss on Derivatives
Accumulated Other Comprehensive Income (Loss)
Balance at Beginning of Period	(225.2)	(127.0)	(270.7)	(73.7)
Other Comprehensive Income (Loss) Before Reclassifications	(58.3)	(34.2)	(10.8)	(83.1)
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	(1.5)	(3.4)	(3.5)	(7.8)
Net Other Comprehensive Income	(59.8)	(37.6)	(14.3)	(90.9)
Balance at End of Period	(285.0)	(164.6)	(285.0)	(164.6)
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss)
Balance at Beginning of Period	(300.7)	(332.6)	(343.0)	(321.1)
Other Comprehensive Income (Loss) Before Reclassifications	80.0	4.2	122.3	(7.3)
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	0.0	0.0	0.0	0.0
Net Other Comprehensive Income	80.0	4.2	122.3	(7.3)
Balance at End of Period	(220.7)	(328.4)	(220.7)	(328.4)
Unrecognized Pension and Postretirement Benefit Costs
Accumulated Other Comprehensive Income (Loss)
Balance at Beginning of Period	(338.8)	(344.9)	(340.2)	(345.7)
Other Comprehensive Income (Loss) Before Reclassifications	(4.6)	0.0	(6.4)	(2.4)
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	3.2	3.2	6.4	6.4
Net Other Comprehensive Income	(1.4)	3.2	0.0	4.0
Balance at End of Period	$ (340.2)	$ (341.7)	$ (340.2)	$ (341.7)