Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Accumulated Other Comprehensive Income (Loss)
Balance at Beginning of Period	$ (2,940.0)	$ (3,162.3)	$ (3,308.0)	$ (3,448.3)
Other Comprehensive Income (Loss) Before Reclassifications	86.4	(297.9)	443.2	(4.8)
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	(7.4)	(2.6)	(18.6)	4.5
Net Other Comprehensive Income (Loss)	93.8	(295.3)	461.8	(9.3)
Balance at End of Period	(2,846.2)	(3,457.6)	(2,846.2)	(3,457.6)
Net Unrealized Loss on Securities
Accumulated Other Comprehensive Income (Loss)
Balance at Beginning of Period	(2,360.8)	(2,205.2)	(1,919.1)	(3,028.4)
Other Comprehensive Income (Loss) Before Reclassifications	(370.6)	(565.5)	(824.7)	257.9
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	(7.6)	(8.1)	(20.0)	(7.9)
Net Other Comprehensive Income (Loss)	(363.0)	(557.4)	(804.7)	265.8
Balance at End of Period	(2,723.8)	(2,762.6)	(2,723.8)	(2,762.6)
Effect of Change in Discount Rate Assumptions on the LFPB
Accumulated Other Comprehensive Income (Loss)
Balance at Beginning of Period	225.3	(260.0)	(648.4)	313.9
Other Comprehensive Income (Loss) Before Reclassifications	487.0	260.1	1,360.7	(313.8)
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	0.0	0.0	0.0	0.0
Net Other Comprehensive Income (Loss)	487.0	260.1	1,360.7	(313.8)
Balance at End of Period	712.3	0.1	712.3	0.1
Net Gain (Loss) on Derivatives
Accumulated Other Comprehensive Income (Loss)
Balance at Beginning of Period	(127.0)	7.8	(73.7)	(9.6)
Other Comprehensive Income (Loss) Before Reclassifications	(34.2)	(34.1)	(83.1)	(8.5)
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	3.4	7.0	7.8	15.2
Net Other Comprehensive Income (Loss)	(37.6)	(41.1)	(90.9)	(23.7)
Balance at End of Period	(164.6)	(33.3)	(164.6)	(33.3)
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss)
Balance at Beginning of Period	(332.6)	(365.4)	(321.1)	(390.1)
Other Comprehensive Income (Loss) Before Reclassifications	4.2	38.3	(7.3)	63.0
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	0.0	0.0	0.0	0.0
Net Other Comprehensive Income (Loss)	4.2	38.3	(7.3)	63.0
Balance at End of Period	(328.4)	(327.1)	(328.4)	(327.1)
Unrecognized Pension and Postretirement Benefit Costs
Accumulated Other Comprehensive Income (Loss)
Balance at Beginning of Period	(344.9)	(339.5)	(345.7)	(334.1)
Other Comprehensive Income (Loss) Before Reclassifications	0.0	3.3	(2.4)	(3.4)
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	(3.2)	(1.5)	(6.4)	(2.8)
Net Other Comprehensive Income (Loss)	3.2	4.8	4.0	(0.6)
Balance at End of Period	$ (341.7)	$ (334.7)	$ (341.7)	$ (334.7)