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Retirement Benefits (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Defined Benefit Pension Plans    
Defined Benefit Plan Disclosure [Line Items]    
Service cost $ 83.7 $ 83.8
Interest cost 172.8 165.0
Expected return on plan assets (269.5) (277.6)
Amortization of prior service cost 0.5 0.5
Recognized actuarial gain (loss) 20.9 30.6
Net periodic cost 8.4 2.3
Retiree Health Benefit Plans    
Defined Benefit Plan Disclosure [Line Items]    
Service cost 8.3 8.2
Interest cost 15.8 15.5
Expected return on plan assets (46.2) (48.1)
Amortization of prior service cost (0.1) (1.4)
Recognized actuarial gain (loss) (0.8) (0.6)
Net periodic cost $ (23.0) $ (26.4)