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Employee Benefits - Plan Assets (Details) - USD ($) $ in Millions | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | --- | ---
Pension Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | $ 3,328.9 | $ 3,225.0 | $ 3,007.0
Pension Plan | Level 1, 2, and 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 1,918.0 | 1,955.0 |
Pension Plan | Level 1, 2, and 3 | United States equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 417.1 | 439.2 |
Pension Plan | Level 1, 2, and 3 | International equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 313.7 | 345.1 |
Pension Plan | Level 1, 2, and 3 | United States bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 1,068.7 | 1,056.4 |
Pension Plan | Level 1, 2, and 3 | International bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 118.5 | 114.3 |
Pension Plan | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 730.8 | 784.3 |
Pension Plan | Level 1 | United States equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 417.1 | 439.2 |
Pension Plan | Level 1 | International equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 313.7 | 345.1 |
Pension Plan | Level 1 | United States bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 0.0 | 0.0 |
Pension Plan | Level 1 | International bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 0.0 | 0.0 |
Pension Plan | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 1,187.2 | 1,170.7 |
Pension Plan | Level 2 | United States equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 0.0 | 0.0 |
Pension Plan | Level 2 | International equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 0.0 | 0.0 |
Pension Plan | Level 2 | United States bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 1,068.7 | 1,056.4 |
Pension Plan | Level 2 | International bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 118.5 | 114.3 |
Pension Plan | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 0.0 | 0.0 |
Pension Plan | Level 3 | United States equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 0.0 | 0.0 |
Pension Plan | Level 3 | International equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 0.0 | 0.0 |
Pension Plan | Level 3 | United States bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 0.0 | 0.0 |
Pension Plan | Level 3 | International bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 0.0 | 0.0 |
Pension Plan | Investments measured at net asset value per share |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 1,410.9 | 1,270.0 |
OPEB Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 1,000.2 | 951.4 | $ 879.6
OPEB Plan | Level 1, 2, and 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 617.4 | 597.2 |
OPEB Plan | Level 1, 2, and 3 | United States equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 135.4 | 141.4 |
OPEB Plan | Level 1, 2, and 3 | International equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 109.1 | 120.9 |
OPEB Plan | Level 1, 2, and 3 | United States bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 357.3 | 322.9 |
OPEB Plan | Level 1, 2, and 3 | International bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 15.6 | 12.0 |
OPEB Plan | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 409.5 | 405.3 |
OPEB Plan | Level 1 | United States equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 135.4 | 141.4 |
OPEB Plan | Level 1 | International equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 109.1 | 120.9 |
OPEB Plan | Level 1 | United States bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 165.0 | 143.0 |
OPEB Plan | Level 1 | International bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 0.0 | 0.0 |
OPEB Plan | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 207.9 | 191.9 |
OPEB Plan | Level 2 | United States equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 0.0 | 0.0 |
OPEB Plan | Level 2 | International equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 0.0 | 0.0 |
OPEB Plan | Level 2 | United States bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 192.3 | 179.9 |
OPEB Plan | Level 2 | International bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 15.6 | 12.0 |
OPEB Plan | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 0.0 | 0.0 |
OPEB Plan | Level 3 | United States equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 0.0 | 0.0 |
OPEB Plan | Level 3 | International equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 0.0 | 0.0 |
OPEB Plan | Level 3 | United States bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 0.0 | 0.0 |
OPEB Plan | Level 3 | International bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 0.0 | 0.0 |
OPEB Plan | Investments measured at net asset value per share |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | $ 382.8 | $ 354.2 |

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