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Pension and Other Postretirement Benefits - Fair Value Hierarchy (Details) - Pension - USD ($) $ in Millions | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | $ 329.7 | $ 318.8 | $ 295.8
Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 | 318.8 |
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 | 329.7 | 0.0 |
Cash |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 2.5 |  |
Cash | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 |  |
Cash | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 |  |
Cash | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 |  |
Cash | Assets measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 2.5 |  |
Return Seeking Assets |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 245.6 |  |
Return Seeking Assets | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 |  |
Return Seeking Assets | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 |  |
Return Seeking Assets | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 |  |
Return Seeking Assets | Assets measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 245.6 |  |
Global equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 167.8 |  |
Global equity | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 |  |
Global equity | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 |  |
Global equity | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 |  |
Global equity | Assets measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 167.8 |  |
Diversified credit |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 49.2 |  |
Diversified credit | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 |  |
Diversified credit | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 |  |
Diversified credit | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 |  |
Diversified credit | Assets measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 49.2 |  |
Real assets |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 28.6 |  |
Real assets | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 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 |  |
Real assets | Assets measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 28.6 |  |
Liability hedging assets |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 81.6 |  |
Liability hedging assets | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 |  |
Liability hedging assets | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 |  |
Liability hedging assets | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | 0.0 |  |
Liability hedging assets | Assets measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets | $ 81.6 |  |
U.S. equities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets |  | 98.4 |
U.S. equities | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets |  | 98.4 |
U.S. equities | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets |  | 0.0 |
U.S. equities | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets |  | 0.0 |
U.S. equities | Assets measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets |  | 0.0 |
International equities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets |  | 86.8 |
International equities | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets |  | 86.8 |
International equities | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets |  | 0.0 |
International equities | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets |  | 0.0 |
International equities | Assets measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets |  | 0.0 |
Fixed income |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets |  | 133.6 |
Fixed income | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets |  | 133.6 |
Fixed income | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets |  | 0.0 |
Fixed income | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets |  | 0.0 |
Fixed income | Assets measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of assets |  | $ 0.0 |

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