Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Accumulated Other Comprehensive Income (Loss)
Balance at Beginning of Period	$ (2,846.2)	$ (3,457.6)	$ (3,308.0)	$ (3,448.3)
Other Comprehensive Income (Loss) Before Reclassifications	109.6	282.8	552.8	278.0
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	6.9	24.2	25.5	19.7
Net Other Comprehensive Income	116.5	307.0	578.3	297.7
Balance at End of Period	(2,729.7)	(3,150.6)	(2,729.7)	(3,150.6)
Net Unrealized Loss on Securities
Accumulated Other Comprehensive Income (Loss)
Balance at Beginning of Period	(2,723.8)	(2,762.6)	(1,919.1)	(3,028.4)
Other Comprehensive Income (Loss) Before Reclassifications	1,225.8	(1,215.1)	401.1	(957.2)
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	6.8	29.3	26.8	37.2
Net Other Comprehensive Income	1,232.6	(1,185.8)	427.9	(920.0)
Balance at End of Period	(1,491.2)	(3,948.4)	(1,491.2)	(3,948.4)
Effect of Change in Discount Rate Assumptions on the LFPB
Accumulated Other Comprehensive Income (Loss)
Balance at Beginning of Period	712.3	0.1	(648.4)	313.9
Other Comprehensive Income (Loss) Before Reclassifications	(1,239.3)	1,688.4	121.4	1,374.6
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	0.0	0.0	0.0	0.0
Net Other Comprehensive Income	(1,239.3)	1,688.4	121.4	1,374.6
Balance at End of Period	(527.0)	1,688.5	(527.0)	1,688.5
Net Loss on Derivatives
Accumulated Other Comprehensive Income (Loss)
Balance at Beginning of Period	(164.6)	(33.3)	(73.7)	(9.6)
Other Comprehensive Income (Loss) Before Reclassifications	58.8	(137.9)	(24.3)	(146.4)
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	(3.1)	(6.5)	(10.9)	(21.7)
Net Other Comprehensive Income	55.7	(144.4)	(35.2)	(168.1)
Balance at End of Period	(108.9)	(177.7)	(108.9)	(177.7)
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss)
Balance at Beginning of Period	(328.4)	(327.1)	(321.1)	(390.1)
Other Comprehensive Income (Loss) Before Reclassifications	68.5	(55.1)	61.2	7.9
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	0.0	0.0	0.0	0.0
Net Other Comprehensive Income	68.5	(55.1)	61.2	7.9
Balance at End of Period	(259.9)	(382.2)	(259.9)	(382.2)
Unrecognized Pension and Postretirement Benefit Costs
Accumulated Other Comprehensive Income (Loss)
Balance at Beginning of Period	(341.7)	(334.7)	(345.7)	(334.1)
Other Comprehensive Income (Loss) Before Reclassifications	(4.2)	2.5	(6.6)	(0.9)
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	3.2	1.4	9.6	4.2
Net Other Comprehensive Income	(1.0)	3.9	3.0	3.3
Balance at End of Period	$ (342.7)	$ (330.8)	$ (342.7)	$ (330.8)