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PENSION AND POST-RETIREMENT PLANS - AMOUNTS INCLUDED IN FINANCIAL STATEMENTS (Details) - USD ($) $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Employee benefit plans |  |  |
Non-current assets | $ 34.8 | $ 18.9 |
Non-current liabilities | (21.8) | (17.8) |
Pension Benefits |  |  |
Employee benefit plans |  |  |
Projected benefit obligations | 193.1 | 187.4 | $ 249.5
Fair value of plan assets at end of year | 227.9 | 206.3 | 238.9
Pension Benefits | Qualified Plan |  |  |
Employee benefit plans |  |  |
Non-current assets | 34.8 | 18.9 |
Total | 34.8 | 18.9 |
Net (loss) gain, net of taxes | (20.3) | (25.8) |
Total | (20.3) | (25.8) |
Pension Benefits | Nonqualified Plan |  |  |
Employee benefit plans |  |  |
Current liabilities | (1.2) | (0.7) |
Non-current liabilities | (3.4) | (3.4) |
Total | (4.6) | (4.1) |
Net (loss) gain, net of taxes | (0.2) | 0.1 |
Total | (0.2) | 0.1 |
Post-retirement benefits |  |  |
Employee benefit plans |  |  |
Projected benefit obligations | $ 19.5 | 15.3 | $ 29.3
Amortization period of unrecognized gains and losses | 5 years |  |
Post-retirement benefits | Qualified Plan |  |  |
Employee benefit plans |  |  |
Current liabilities | $ (1.1) | (0.9) |
Non-current liabilities | (18.4) | (14.4) |
Total | (19.5) | (15.3) |
Net (loss) gain, net of taxes | 2.7 | 7.6 |
Prior service credit, net of taxes | 8.3 | 11.1 |
Total | $ 11.0 | $ 18.7 |

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