| **Pension and Other Post-retirement Benefits - Reconciliation of Fair Value Measurements Using Significant Unobservable Inputs (Details) - USD ($) $ in Millions** | 12 Months Ended |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------|
||
| **Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]**                                                               |            |   |
| Plan assets at beginning of year                                                                                                                                   | $ 857.3         |   |
| Relating to assets still held at the reporting date                                                                                                                | 3.8             | $ (4.7) |
| Relating to assets sold during the period                                                                                                                          | 5.2             | (0.1) |
| Purchases, sales and settlements                                                                                                                                   | (88.6)          | (1.4) |
| Plan assets at end of year                                                                                                                                         | 822.4           | 857.3 |
| Real estate                                                                                                                                                        |            |   |
| **Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]**                                                               |            |   |
| Plan assets at beginning of year                                                                                                                                   | 79.8            |   |
| Relating to assets still held at the reporting date                                                                                                                | 0.0             | (2.5) |
| Relating to assets sold during the period                                                                                                                          | 8.3             | 0.0 |
| Purchases, sales and settlements                                                                                                                                   | (88.1)          | 0.0 |
| Plan assets at end of year                                                                                                                                         | 0.0             | 79.8 |
| Private equity                                                                                                                                                     |            |   |
| **Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]**                                                               |            |   |
| Plan assets at beginning of year                                                                                                                                   | 4.9             |   |
| Relating to assets still held at the reporting date                                                                                                                | 3.8             | (2.2) |
| Relating to assets sold during the period                                                                                                                          | (3.1)           | (0.1) |
| Purchases, sales and settlements                                                                                                                                   | (0.5)           | (1.4) |
| Plan assets at end of year                                                                                                                                         | 5.1             | 4.9 |
| Significant Non- observable Inputs (Level 3)                                                                                                                       |            |   |
| **Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]**                                                               |            |   |
| Plan assets at beginning of year                                                                                                                                   | 84.7            | 90.9 |
| Plan assets at end of year                                                                                                                                         | 5.1             | 84.7 |
| Significant Non- observable Inputs (Level 3) | Real estate                                                                                                         |            |   |
| **Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]**                                                               |            |   |
| Plan assets at beginning of year                                                                                                                                   | 79.8            | 82.3 |
| Plan assets at end of year                                                                                                                                         | 0.0             | 79.8 |
| Significant Non- observable Inputs (Level 3) | Private equity                                                                                                      |            |   |
| **Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]**                                                               |            |   |
| Plan assets at beginning of year                                                                                                                                   | 4.9             | 8.6 |
| Plan assets at end of year                                                                                                                                         | $ 5.1           | $ 4.9 |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets sold.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets still held.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                            |
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| - Definition
A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.
+ 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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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, measured using unobservable input, of increase (decrease) in plan asset of defined benefit plan from purchase, sale and settlement of trade associated with underlying investment.
+ References
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| X                                                                                                                                                                          |
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