Revenue Recognition - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Disaggregation of Revenue [Line Items]
Accounts receivable, credit loss expense (reversal)		$ 0
Revenue	$ 1,364,000,000	691,400,000
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue	1,364,000,000	691,400,000
Corporate and Other (1)
Disaggregation of Revenue [Line Items]
Revenue	174,400,000	(335,400,000)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue	174,400,000	(335,400,000)
Designated as Hedging Instrument
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax	99,200,000	(286,900,000)
Trade receivables
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Accounts receivable, allowance for credit loss	0		$ 0
Accounts receivable, allowance for credit loss	0		0
Miscellaneous Receivables
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Accounts receivable, allowance for credit loss	0		0
Accounts receivable, allowance for credit loss	0		$ 0
Coal Contract and Physical commodity purchase / sale contracts | Designated as Hedging Instrument
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax	$ 118,700,000	$ (301,000,000.0)