| **Pension and Other Post-retirement Benefits - Fair Value Measurement of Plan Assets (Details) - USD ($) $ in Millions** | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019 |
|--------------------------------------------------------------------------------------------------------------------------|---------------|---------------|---------------|
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | $ 822.4       | $ 857.3       |          |
| Non-investment plan assets                                                                                               | 3.5           | 1.5           |          |
| Total plan assets                                                                                                        | 825.9         | 858.8         |          |
| Short-term investments                                                                                                   |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 182.9         | 13.7          |          |
| Common stocks                                                                                                            |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 3.7           | 136.5         |          |
| Commingled equity funds                                                                                                  |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | 132.0         |          |
| U.S. Treasury securities                                                                                                 |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 52.8          | 44.3          |          |
| Other fixed income securities                                                                                            |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 551.2         | 229.1         |          |
| Commingled fixed income funds                                                                                            |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | 119.5         |          |
| Options                                                                                                                  |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | (8.1)         |          |
| Mutual funds                                                                                                             |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 26.7          | 105.6         |          |
| Real estate funds                                                                                                        |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | 79.8          |          |
| Private equity                                                                                                           |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 5.1           | 4.9           |          |
| Quoted Prices in Active Markets for Identical Contracts (Level 1)                                                        |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 239.4         | 180.8         |          |
| Quoted Prices in Active Markets for Identical Contracts (Level 1) | Short-term investments                               |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 182.9         | 0.0           |          |
| Quoted Prices in Active Markets for Identical Contracts (Level 1) | Common stocks                                        |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 3.7           | 136.5         |          |
| Quoted Prices in Active Markets for Identical Contracts (Level 1) | Commingled equity funds                              |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | 0.0           |          |
| Quoted Prices in Active Markets for Identical Contracts (Level 1) | U.S. Treasury securities                             |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 52.8          | 44.3          |          |
| Quoted Prices in Active Markets for Identical Contracts (Level 1) | Other fixed income securities                        |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | 0.0           |          |
| Quoted Prices in Active Markets for Identical Contracts (Level 1) | Commingled fixed income funds                        |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | 0.0           |          |
| Quoted Prices in Active Markets for Identical Contracts (Level 1) | Options                                              |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | 0.0           |          |
| Quoted Prices in Active Markets for Identical Contracts (Level 1) | Mutual funds                                         |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | 0.0           |          |
| Quoted Prices in Active Markets for Identical Contracts (Level 1) | Real estate funds                                    |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | 0.0           |          |
| Quoted Prices in Active Markets for Identical Contracts (Level 1) | Private equity                                       |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | 0.0           |          |
| Significant Other Observable Inputs (Level 2)                                                                            |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 577.9         | 591.8         |          |
| Significant Other Observable Inputs (Level 2) | Short-term investments                                                   |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | 13.7          |          |
| Significant Other Observable Inputs (Level 2) | Common stocks                                                            |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | 0.0           |          |
| Significant Other Observable Inputs (Level 2) | Commingled equity funds                                                  |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | 132.0         |          |
| Significant Other Observable Inputs (Level 2) | U.S. Treasury securities                                                 |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | 0.0           |          |
| Significant Other Observable Inputs (Level 2) | Other fixed income securities                                            |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 551.2         | 229.1         |          |
| Significant Other Observable Inputs (Level 2) | Commingled fixed income funds                                            |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | 119.5         |          |
| Significant Other Observable Inputs (Level 2) | Options                                                                  |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | (8.1)         |          |
| Significant Other Observable Inputs (Level 2) | Mutual funds                                                             |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 26.7          | 105.6         |          |
| Significant Other Observable Inputs (Level 2) | Real estate funds                                                        |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | 0.0           |          |
| Significant Other Observable Inputs (Level 2) | Private equity                                                           |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | 0.0           |          |
| Significant Non- observable Inputs (Level 3)                                                                             |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 5.1           | 84.7          | $ 90.9        |
| Significant Non- observable Inputs (Level 3) | Short-term investments                                                    |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | 0.0           |          |
| Significant Non- observable Inputs (Level 3) | Common stocks                                                             |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | 0.0           |          |
| Significant Non- observable Inputs (Level 3) | Commingled equity funds                                                   |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | 0.0           |          |
| Significant Non- observable Inputs (Level 3) | U.S. Treasury securities                                                  |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | 0.0           |          |
| Significant Non- observable Inputs (Level 3) | Other fixed income securities                                             |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | 0.0           |          |
| Significant Non- observable Inputs (Level 3) | Commingled fixed income funds                                             |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | 0.0           |          |
| Significant Non- observable Inputs (Level 3) | Options                                                                   |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | 0.0           |          |
| Significant Non- observable Inputs (Level 3) | Mutual funds                                                              |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | 0.0           |          |
| Significant Non- observable Inputs (Level 3) | Real estate funds                                                         |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | 0.0           | 79.8          | 82.3          |
| Significant Non- observable Inputs (Level 3) | Private equity                                                            |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                         |          |          |          |
| Total fair value of plan asset investments                                                                               | $ 5.1         | $ 4.9         | $ 8.6         |

| X                                                                                                                                                                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Defined benefit plan fair value of non-investment plan assets.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                              |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Defined Benefit Plan Fair Value of Plan Assets Including Non-Investment Plan Assets
+ References
No definition available.
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| - Definition
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
+ References
No definition available.
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.
+ References
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