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Derivatives and Fair Value Measurements - Narrative (Details) t in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2023 USD ($) t $ / $	Mar. 31, 2022 USD ($)	Mar. 31, 2023 AUD ($) $ / $	Dec. 31, 2022 USD ($)
Derivatives, Fair Value [Line Items]
Unobservable Measurement Input, Uncertainty, Description	10
Asset impairment	$ 2.0	$ 0.0
Fair Value, Inputs, Level 1, 2 and 3
Derivatives, Fair Value [Line Items]
Derivative assets (liabilities), at fair value	0.0	0.0
Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Variation margin posted (received)	(48.8)			$ (209.7)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax	99.2	(286.9)
Foreign currency option contracts
Derivatives, Fair Value [Line Items]
Notional amount	$ 350.0		$ 632,000,000
Derivative, Floor Price			0.63
Derivative, Cap Price			0.73
Foreign currency option contracts \| Minimum
Derivatives, Fair Value [Line Items]
Derivative, exchange rate cap (in dollars per share) \| $ / $	0.70		0.70
Foreign currency option contracts \| Maximum
Derivatives, Fair Value [Line Items]
Derivative, exchange rate cap (in dollars per share) \| $ / $	0.75		0.75
Foreign currency option contracts \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax	$ (2.2)	3.3
Financial trading contracts
Derivatives, Fair Value [Line Items]
Derivative notional amount (in tonnes) \| t	0.3
Financial trading contracts \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax	$ (17.3)	10.8
Diesel Fuel Hedge Contracts
Derivatives, Fair Value [Line Items]
Notional amount			$ 0
Coal Contract and Physical commodity purchase / sale contracts \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax	118.7	(301.0)
Gain (Loss) on Derivative Instruments \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax		(237.0)
Forward Contracts \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax	0.0	64.0
Derivative contracts related to forecasted sales \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax	118.7	$ (301.0)
Variation Margin Cash \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Variation margin posted (received)	48.8			198.0
Total Margin Posted
Derivatives, Fair Value [Line Items]
Derivative Liability, Subject to Master Netting Arrangement, Collateral, Right to Reclaim Cash Not Offset	59.8			255.5
Initial Margin Posted
Derivatives, Fair Value [Line Items]
Derivative Liability, Subject to Master Netting Arrangement, Collateral, Right to Reclaim Cash Not Offset	$ 11.0			$ 57.5