Long-term Debt - Schedule of Debt (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Finance lease obligations	$ 30.4	$ 27.3
Less: Debt issuance costs	(45.1)	(42.7)
Total debt	1,328.2	1,547.8
Less: Current portion of long-term debt	59.5	44.9
Long-term debt	1,268.7	1,502.9
Senior Notes \| 6.000% Senior Secured Notes due March 2022 (2022 Notes)
Debt Instrument [Line Items]
Long-term debt	$ 23.1	459.0
Stated interest rate	6.00%
Senior Notes \| 8.500% Senior Secured Notes due December 2024 (Peabody Notes)
Debt Instrument [Line Items]
Long-term debt	$ 128.8	0.0
Stated interest rate	8.50%
Senior Notes \| 10.000% Senior Secured Notes due December 2024 (Co-Issuer Notes)
Debt Instrument [Line Items]
Long-term debt	$ 193.9	0.0
Stated interest rate	10.00%
Senior Notes \| 6.375% Senior Secured Notes due March 2025 (2025 Notes)
Debt Instrument [Line Items]
Long-term debt	$ 462.4	500.0
Stated interest rate	6.375%
Term Loan \| Senior Secured Term Loan due 2024 (Co-Issuer Term Loans)
Debt Instrument [Line Items]
Long-term debt	$ 206.0	0.0
Stated interest rate	10.00%
Term Loan \| Senior Secured Term Loan due 2025, net of original issue discount (Senior Secured Term Loan)
Debt Instrument [Line Items]
Long-term debt	$ 328.7	388.2
Line of credit \| Revolving credit facility
Debt Instrument [Line Items]
Long-term debt	$ 0.0	$ 216.0

Amount of short-term and long-term debt and lease obligation.

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Present value of lessee's discounted obligation for lease payments from finance lease.

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Amount of long-term debt and lease obligation, classified as noncurrent.

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Amount of long-term debt and lease obligation, classified as current.

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