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Postretirement Benefit Plans (Debt Securities, Trading, and Equity Securities, FV-NI) (Details) - USD ($)
$ in Millions
 3 Months Ended 12 Months Ended
Mar. 31, 2026
Dec. 31, 2025
Defined Benefit Plan Disclosure [Line Items]    
Adjusted Cost $ 4.0 $ 4.2
Unrealized Gains 0.6 0.7
Unrealized Losses (0.1) (0.1)
Fair Value 4.5 4.8
Level 1 Securities:    
Defined Benefit Plan Disclosure [Line Items]    
Adjusted Cost 3.9 4.1
Unrealized Gains 0.6 0.7
Unrealized Losses (0.1) (0.1)
Fair Value 4.4 4.7
Level 2 Securities:    
Defined Benefit Plan Disclosure [Line Items]    
Adjusted Cost 0.1 0.1
Unrealized Gains 0.0 0.0
Unrealized Losses 0.0 0.0
Fair Value $ 0.1 $ 0.1