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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

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