Property, Plant, Equipment and Mine Development - (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Property, Plant, Equipment and Mine Development[Line Items]
Less: Accumulated depreciation, depletion and amortization	$ (2,372.5)	$ (2,066.3)
Property, plant, equipment and mine development, net	3,081.5	2,844.1
Coal reserves	1,100.0	1,200.0
Coal reserves not subject to depletion	100.0	100.0
Land and coal interests
Property, Plant, Equipment and Mine Development[Line Items]
Property, plant equipment and mine development, gross	2,648.5	2,475.2
Buildings and improvements
Property, Plant, Equipment and Mine Development[Line Items]
Property, plant equipment and mine development, gross	726.7	647.6
Machinery and equipment
Property, Plant, Equipment and Mine Development[Line Items]
Property, plant equipment and mine development, gross	2,078.8	1,787.6
Coal Reserves Held by Fee Ownership
Property, Plant, Equipment and Mine Development[Line Items]
Coal reserves	500.0	500.0
Coal reserves and resources comprised of mineral rights for leased coal interests and advance royalties
Property, Plant, Equipment and Mine Development[Line Items]
Coal reserves	$ 600.0	$ 700.0

Net book value of coal reserves.

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Coal reserves not subject to depletion.

+ References

No definition available.

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- Definition

Amount of accumulated depreciation and amortization from plant, property, and equipment and right-of-use asset from finance lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 360
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482099/360-10-50-1

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Accounting Standards Codification
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-Paragraph 4
-Subparagraph (a)
-SubTopic 20
-Topic 842
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479041/842-20-45-4

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
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-Subparagraph (a)
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-4

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- Definition

Amount, after accumulated depreciation and amortization, of property, plant, and equipment and finance lease right-of-use asset.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 360
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482099/360-10-50-1

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-4

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- Definition

Amount, before accumulated depreciation and amortization, of property, plant, and equipment and finance lease right-of-use asset.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 360
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482099/360-10-50-1

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 210
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Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Subparagraph (a)
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-Topic 842
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479041/842-20-45-1

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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