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Pension and Other Postretirement Benefits - Fair Value Hierarchy (Details) - Pension - USD ($) $ in Millions | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
--- | --- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | $ 224.8 | $ 216.6 | $ 329.7
Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 | 0.0 |
Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 | 0.0 |
Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 | 0.0 |
Assets measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 224.8 | 216.6 |
Cash |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 4.6 | 1.3 |
Cash | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 | 0.0 |
Cash | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 | 0.0 |
Cash | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 | 0.0 |
Cash | Assets measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 4.6 | 1.3 |
Global equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 100.0 | 99.0 |
Global equity | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 | 0.0 |
Global equity | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 | 0.0 |
Global equity | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 | 0.0 |
Global equity | Assets measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 100.0 | 99.0 |
Diversified credit |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 34.7 | 40.1 |
Diversified credit | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 | 0.0 |
Diversified credit | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 | 0.0 |
Diversified credit | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 | 0.0 |
Diversified credit | Assets measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 34.7 | 40.1 |
Real assets |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 22.8 | 30.4 |
Real assets | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 | 0.0 |
Real assets | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 |  |
Real assets | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 | 0.0 |
Real assets | Assets measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 22.8 | 30.4 |
Liability hedging assets |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 62.7 | 45.8 |
Liability hedging assets | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 | 0.0 |
Liability hedging assets | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 | 0.0 |
Liability hedging assets | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 | 0.0 |
Liability hedging assets | Assets measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | $ 62.7 | $ 45.8 |

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