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Revenue Recognition - Revenue by Product Type and Market (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2024 | Jun. 30, 2023 | Jun. 30, 2024 | Jun. 30, 2023
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | $ 1,042.0 | $ 1,268.8 | $ 2,025.6 | $ 2,632.8
Other Income | 4.2 | 3.8 | 9.1 | 25.6
Designated as Hedging Instrument |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax | 2.4 | 29.3 | (3.3) | 128.5
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net | (1.6) | (19.3) | (2.4) | (55.5)
Derivative, Gain (Loss) on Derivative, Net | 0.8 | 10.0 | (5.7) | 73.0
Physical commodity purchase / sale contracts [Member] | Designated as Hedging Instrument |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax |  | 40.3 |  | 159.0
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net | 0.0 | (30.3) | 0.0 | (80.9)
Derivative, Gain (Loss) on Derivative, Net |  | 10.0 |  | 78.1
Coal Contract [Member] | Designated as Hedging Instrument |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax |  | (13.8) |  | (31.1)
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net |  | 13.9 |  | 31.2
Derivative, Gain (Loss) on Derivative, Net | 0.0 | 0.1 | 0.0 | 0.1
Coal Contract and Physical commodity purchase / sale contracts | Designated as Hedging Instrument |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax | 0.0 | 40.3 | 0.0 | 159.0
Thermal coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 729.2 | 857.4 | 1,445.0 | 1,756.6
Metallurgical coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 294.0 | 371.6 | 538.0 | 658.8
Other (2) |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 18.8 | 39.8 | 42.6 | 217.4
Domestic | Thermal coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 458.6 | 489.9 | 931.3 | 1,080.3
Export | Thermal coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 270.6 | 367.5 | 513.7 | 676.3
Export | Metallurgical coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 294.0 | 371.6 | 538.0 | 658.8
Seaborne Thermal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 307.5 | 399.5 | 591.4 | 746.0
Seaborne Thermal | Thermal coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 307.5 | 399.4 | 591.2 | 745.7
Seaborne Thermal | Metallurgical coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 0.0 | 0.0 | 0.0 | 0.0
Seaborne Thermal | Other (2) |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 0.0 | 0.1 | 0.2 | 0.3
Seaborne Thermal | Domestic | Thermal coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 36.9 | 31.9 | 77.5 | 69.4
Seaborne Thermal | Export | Thermal coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 270.6 | 367.5 | 513.7 | 676.3
Seaborne Thermal | Export | Metallurgical coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 0.0 | 0.0 | 0.0 | 0.0
Seaborne Metallurgical |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 294.3 | 372.5 | 541.3 | 660.9
Seaborne Metallurgical | Thermal coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 0.0 | 0.0 | 0.0 | 0.0
Seaborne Metallurgical | Metallurgical coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 294.0 | 371.6 | 538.0 | 658.8
Seaborne Metallurgical | Other (2) |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 0.3 | 0.9 | 3.3 | 2.1
Seaborne Metallurgical | Domestic | Thermal coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 0.0 | 0.0 | 0.0 | 0.0
Seaborne Metallurgical | Export | Thermal coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 0.0 | 0.0 | 0.0 | 0.0
Seaborne Metallurgical | Export | Metallurgical coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 294.0 | 371.6 | 538.0 | 658.8
Powder River Basin |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 221.9 | 259.7 | 476.0 | 565.0
Powder River Basin | Thermal coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 221.4 | 259.8 | 475.5 | 564.8
Powder River Basin | Metallurgical coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 0.0 | 0.0 | 0.0 | 0.0
Powder River Basin | Other (2) |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 0.5 | (0.1) | 0.5 | 0.2
Powder River Basin | Domestic | Thermal coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 221.4 | 259.8 | 475.5 | 564.8
Powder River Basin | Export | Thermal coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 0.0 | 0.0 | 0.0 | 0.0
Powder River Basin | Export | Metallurgical coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 0.0 | 0.0 | 0.0 | 0.0
Other U.S. Thermal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 202.0 | 199.9 | 393.6 | 449.3
Other U.S. Thermal | Thermal coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 200.3 | 198.2 | 378.3 | 446.1
Other U.S. Thermal | Metallurgical coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 0.0 | 0.0 | 0.0 | 0.0
Other U.S. Thermal | Other (2) |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 1.7 | 1.7 | 15.3 | 3.2
Other U.S. Thermal | Domestic | Thermal coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 200.3 | 198.2 | 378.3 | 446.1
Other U.S. Thermal | Export | Thermal coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 0.0 | 0.0 | 0.0 | 0.0
Other U.S. Thermal | Export | Metallurgical coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 0.0 | 0.0 | 0.0 | 0.0
Corporate and Other (1) |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 16.3 | 37.2 | 23.3 | 211.6
Corporate and Other (1) | Thermal coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 0.0 | 0.0 | 0.0 | 0.0
Corporate and Other (1) | Trading and Brokerage Coal Deliveries |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 12.1 | 23.3 | 14.2 | 107.8
Corporate and Other (1) | Metallurgical coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 0.0 | 0.0 | 0.0 | 0.0
Corporate and Other (1) | Other (2) |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 16.3 | 37.2 | 23.3 | 211.6
Corporate and Other (1) | Domestic | Thermal coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 0.0 | 0.0 | 0.0 | 0.0
Corporate and Other (1) | Export | Thermal coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 0.0 | 0.0 | 0.0 | 0.0
Corporate and Other (1) | Export | Metallurgical coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | $ 0.0 | $ 0.0 | $ 0.0 | $ 0.0

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