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Retirement Benefits - Narrative (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 USD ($) employee | Dec. 31, 2021 USD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 | Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |
Projected Retirement Benefit Expense In Next 12 months |  | $ 74.0 |  |  |  |
Defined Contribution Plan, Cost |  | $ 31.1 | $ 20.4 | $ 29.9 |  |
Termination benefits |  |  |  | 17.4 |  |
Multiemployer Plans, Withdrawal Obligation, Payment Period |  | 15 years |  |  |  |
Income tax provision |  | $ 15.5 | 26.8 | 77.7 |  |
Settlement loss (gain) included in net income (loss) |  | 29.5 | (21.9) | 0.0 |  |
Reclassification out of Accumulated Other Comprehensive Income [Member] | Post- retirement benefit plans [Member] |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |
Income tax provision |  | (12.0) | (11.9) | (19.7) |  |
Settlement loss (gain) included in net income (loss) |  | 29.5 | (21.9) | 0.0 |  |
Collective-Bargaining Arrangement, Other |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |
Income tax provision |  |  | 15.5 |  |  |
Other Postretirement Benefits |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |
Curtailment loss (gain) |  | 0.0 | 0.0 | (0.2) |  |
Employer contributions |  | 0.0 | 0.0 |  |  |
Projected Retirement Benefit Expense In Next 12 months |  | 16.0 |  |  |  |
Defined Contribution Plan, Cost |  | $ 1.0 | $ 0.0 | $ 0.7 |  |
Assumed increase in per capita cost of covered benefits in next 12 months |  | 7.80% |  |  |  |
Assumed ultimate health care cost trend rate |  | 4.00% |  |  |  |
Expected long-term rate of return on assets |  | 0.00% | 0.00% | 0.00% |  |
Fair value of plan assets |  | $ 0.0 | $ 0.0 | $ 0.0 |  |
Termination benefits |  | 0.0 | 0.0 | 6.7 |  |
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement |  | 0.0 | 43.0 |  |  |
Settlement loss (gain) included in net income (loss) |  | 0.0 | (21.9) |  |  |
Pension Benefits [Member] |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |
Curtailment loss (gain) |  | 0.0 | 0.0 | $ 0.0 |  |
Employer contributions |  | 57.4 | 77.3 |  |  |
Projected Retirement Benefit Expense In Next 12 months |  | 58.0 |  |  |  |
Accumulated benefit obligation |  | $ 1,716.8 | $ 2,398.0 |  |  |
Expected long-term rate of return on assets |  | 6.43% | 6.71% | 7.16% |  |
Actual return on plan assets |  | (14.50%) | 12.40% | 15.20% | 15.10% | (4.80%)
Fair value of plan assets |  | $ 1,599.5 | $ 2,120.9 | $ 2,046.4 |  |
Defined Benefit Plan, Weighted Average Life Expectancy |  | 17 years |  |  |  |
Termination benefits |  | $ 0.0 | 0.0 | 10.9 |  |
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement |  | 0.0 | 0.0 |  |  |
Settlement loss (gain) included in net income (loss) |  | 29.5 | 0.0 |  |  |
Pension Benefits [Member] | Global debt securities and cash [Member] |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |
Unfunded commitments |  | 45.0 |  |  |  |
Pension Benefits [Member] | Private equity [Member] |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |
Unfunded commitments |  | 125.0 |  |  |  |
Fair value of plan assets |  | 224.3 | 176.7 |  |  |
Pension Benefits [Member] | Real estate and other [Member] |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |
Unfunded commitments |  | 29.0 |  |  |  |
Pension Benefits [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |
Fair value of plan assets |  | 0.0 | 0.0 |  |  |
Pension Benefits [Member] | Fair Value, Inputs, Level 3 [Member] | Private equity [Member] |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |
Fair value of plan assets |  | 0.0 | 0.0 |  |  |
Pension Benefits [Member] | Forecast |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |
Expected long-term rate of return on assets | 6.57% |  |  |  |  |
Pension Benefits [Member] | MultiemployerPlan1 [Member] |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |
Multiemployer Plans, Withdrawal Obligation |  | 27.0 |  |  |  |
Pension Benefits [Member] | Nonqualified plans |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |
Estimated employer contributions in next 12 months |  | $ 6.0 |  |  |  |
Pension Benefits [Member] | United States |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |
Defined benefit plan, number of employees accruing benefit service | employee |  | 900 |  |  |  |
Defined Benefit Plan, Percent Of Employees accruing benefit service |  | 7.00% |  |  |  |
Percent reduction in defined benefit plan participation |  | 60.00% |  |  |  |
Employer contributions |  | $ 50.0 | 67.0 | $ 130.0 |  |
Expected future voluntary contributions to pension plan |  | 50.0 |  |  |  |
Estimated employer contributions in next 12 months |  | $ 0.0 |  |  |  |
Percentage of total assets |  | 95.00% |  |  |  |
Small annuity buy out [Member] | Pension Benefits [Member] |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |
Benefits paid |  |  | $ 70.0 |  |  |

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