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Employee Benefits - Plan Assets (Details) - USD ($) $ in Millions | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
--- | --- | --- | ---
Pension Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | $ 2,665.8 | $ 2,628.0 | $ 3,328.9
Pension Plan | Level 1, 2, and 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 1,347.9 | 1,367.4 |
Pension Plan | Level 1, 2, and 3 | United States equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 179.3 | 231.5 |
Pension Plan | Level 1, 2, and 3 | International equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 174.0 | 202.2 |
Pension Plan | Level 1, 2, and 3 | United States bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 906.6 | 838.7 |
Pension Plan | Level 1, 2, and 3 | International bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 88.0 | 95.0 |
Pension Plan | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 353.3 | 433.7 |
Pension Plan | Level 1 | United States equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 179.3 | 231.5 |
Pension Plan | Level 1 | International equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 174.0 | 202.2 |
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 | 994.6 | 933.7 |
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 | 906.6 | 838.7 |
Pension Plan | Level 2 | International bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 88.0 | 95.0 |
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 | Equity securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 407.4 | 466.0 |
Pension Plan | Investments measured at net asset value per share | Fixed income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 124.2 | 101.0 |
Pension Plan | Investments measured at net asset value per share | Other investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 786.3 | 693.6 |
OPEB Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 829.6 | 835.3 | $ 1,000.2
OPEB Plan | Level 1, 2, and 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 483.0 | 464.7 |
OPEB Plan | Level 1, 2, and 3 | United States equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 91.8 | 92.5 |
OPEB Plan | Level 1, 2, and 3 | International equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 84.6 | 83.9 |
OPEB Plan | Level 1, 2, and 3 | United States bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 294.7 | 275.1 |
OPEB Plan | Level 1, 2, and 3 | International bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 11.9 | 13.2 |
OPEB Plan | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 267.9 | 306.2 |
OPEB Plan | Level 1 | United States equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 91.8 | 92.5 |
OPEB Plan | Level 1 | International equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 84.6 | 83.9 |
OPEB Plan | Level 1 | United States bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 91.5 | 129.8 |
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 | 215.1 | 158.5 |
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 | 203.2 | 145.3 |
OPEB Plan | Level 2 | International bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 11.9 | 13.2 |
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 | Equity securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 182.1 | 186.6 |
OPEB Plan | Investments measured at net asset value per share | Fixed income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | 47.7 | 65.5 |
OPEB Plan | Investments measured at net asset value per share | Other investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair Value of Plan Assets | $ 116.8 | $ 118.5 |

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