Long-term Debt - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Mar. 01, 2022
Debt Instrument [Line Items]
Debt issuance cost	$ 8.5			$ 8.5		$ 9.8
Interest expense	13.8	$ 33.8		45.5	$ 110.8
Net loss on early debt extinguishment	0.0	8.7		8.8	34.5
Finance lease obligations	22.1			22.1		23.6
Interest Paid, Capitalized, Investing Activities	$ 14.8	$ 26.4		$ 56.7	$ 104.2
Dividends Payable, Amount Per Share	$ 0.150			$ 0.150
3.250% Convertible Senior Notes due March 2028 (2028 Convertible Notes)
Debt Instrument [Line Items]
Debt Instrument, Convertible, If-converted Value in Excess of Principal				$ 99.0
8.500% Senior Secured Notes due December 20242 and 6.375% Senior Secured Notes due March 2025 [Domain]
Debt Instrument [Line Items]
Net loss on early debt extinguishment			$ 23.0
Senior Notes | 3.250% Convertible Senior Notes due March 2028 (2028 Convertible Notes)
Debt Instrument [Line Items]
Stated interest rate	3.25%			3.25%
Long-term debt	$ 320.0			$ 320.0		$ 320.0
Principal amount							$ 320.0
Debt Issuance Costs, Gross			11.2
Debt Conversion, Converted Instrument, Rate	1.00%
Debt Instrument, Convertible, Conversion Ratio	50.3816
Debt Instrument, Convertible, Conversion Ratio, Revised	50.7205
Senior Notes | 6.375% Senior Secured Notes due March 2025 (2025 Notes)
Debt Instrument [Line Items]
Debt repurchase, amount			257.4
Senior Notes | 8.500% Senior Secured Notes due December 2024 (2024 Peabody Notes)
Debt Instrument [Line Items]
Debt repurchase, amount			$ 62.6