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Pension and Other Postretirement Benefit Plans - Recurring Fair Value Measures (Details) - USD ($) $ in Millions | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
--- | --- | --- | ---
Pension |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | $ 589.0 | $ 568.6 | $ 745.7
Pension | Level 1 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 155.0 | 134.3 |
Pension | Level 2 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 415.1 | 411.9 |
Pension | Level 3 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 18.9 | 22.4 |
Pension | U.S. Large-cap |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 83.7 | 61.2 |
Pension | U.S. Large-cap | Level 1 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Pension | U.S. Large-cap | Level 2 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 83.7 | 61.2 |
Pension | U.S. Large-cap | Level 3 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Pension | U.S. Mid-cap Growth |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 69.9 | 40.0 |
Pension | U.S. Mid-cap Growth | Level 1 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Pension | U.S. Mid-cap Growth | Level 2 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 69.9 | 40.0 |
Pension | U.S. Mid-cap Growth | Level 3 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Pension | U.S. Small-cap |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 46.5 | 35.4 |
Pension | U.S. Small-cap | Level 1 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Pension | U.S. Small-cap | Level 2 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 46.5 | 35.4 |
Pension | U.S. Small-cap | Level 3 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Pension | International |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 134.6 | 127.0 |
Pension | International | Level 1 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 134.6 | 127.0 |
Pension | International | Level 2 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Pension | International | Level 3 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Pension | Fixed Income Securities |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 215.0 | 275.3 |
Pension | Fixed Income Securities | Level 1 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Pension | Fixed Income Securities | Level 2 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 215.0 | 275.3 |
Pension | Fixed Income Securities | Level 3 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Pension | Cash and Cash Equivalents |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 20.4 | 7.3 |
Pension | Cash and Cash Equivalents | Level 1 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 20.4 | 7.3 |
Pension | Cash and Cash Equivalents | Level 2 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Pension | Cash and Cash Equivalents | Level 3 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Pension | Real Estate |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 18.9 | 22.4 |
Pension | Real Estate | Level 1 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Pension | Real Estate | Level 2 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Pension | Real Estate | Level 3 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 18.9 | 22.4 | 21.6
Postretirement Health and Life |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 173.8 | 162.6 | 201.8
Postretirement Health and Life | Level 1 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 173.8 | 162.6 |
Postretirement Health and Life | Level 2 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Postretirement Health and Life | Level 3 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Postretirement Health and Life | U.S. Large-cap |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 30.0 | 26.7 |
Postretirement Health and Life | U.S. Large-cap | Level 1 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 30.0 | 26.7 |
Postretirement Health and Life | U.S. Large-cap | Level 2 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Postretirement Health and Life | U.S. Large-cap | Level 3 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Postretirement Health and Life | U.S. Mid-cap Growth |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 28.7 | 25.5 |
Postretirement Health and Life | U.S. Mid-cap Growth | Level 1 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 28.7 | 25.5 |
Postretirement Health and Life | U.S. Mid-cap Growth | Level 2 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Postretirement Health and Life | U.S. Mid-cap Growth | Level 3 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Postretirement Health and Life | U.S. Small-cap |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 14.9 | 12.7 |
Postretirement Health and Life | U.S. Small-cap | Level 1 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 14.9 | 12.7 |
Postretirement Health and Life | U.S. Small-cap | Level 2 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Postretirement Health and Life | U.S. Small-cap | Level 3 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Postretirement Health and Life | International |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 41.9 | 41.5 |
Postretirement Health and Life | International | Level 1 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 41.9 | 41.5 |
Postretirement Health and Life | International | Level 2 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Postretirement Health and Life | International | Level 3 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Postretirement Health and Life | Cash and Cash Equivalents |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 3.2 | 0.7 |
Postretirement Health and Life | Cash and Cash Equivalents | Level 1 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 3.2 | 0.7 |
Postretirement Health and Life | Cash and Cash Equivalents | Level 2 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Postretirement Health and Life | Cash and Cash Equivalents | Level 3 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Postretirement Health and Life | Private Equity | Level 3 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets |  | 0.0 | $ 2.0
Postretirement Health and Life | Mutual Funds |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 55.1 | 55.5 |
Postretirement Health and Life | Mutual Funds | Level 1 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 55.1 | 55.5 |
Postretirement Health and Life | Mutual Funds | Level 2 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | 0.0 | 0.0 |
Postretirement Health and Life | Mutual Funds | Level 3 |  |  |
Recurring Fair Value Measures [Line Items] |  |  |
Fair Value of Assets | $ 0.0 | $ 0.0 |

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