Property, Plant, Equipment and Mine Development (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Land and coal interests	$ 4,172.0	$ 4,148.8
Buildings and improvements	554.7	559.3
Machinery and equipment	1,556.4	1,456.3
Less: Accumulated depreciation, depletion and amortization	(1,383.9)	(957.4)
Property, plant, equipment and mine development, net	$ 4,899.2	$ 5,207.0

Land and coal interests.

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- Definition

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

+ References

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- Definition

Amount before accumulated depreciation of building structures held for productive use including addition, improvement, or renovation to the structure, including, but not limited to, interior masonry, interior flooring, electrical, and plumbing.

+ References

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- Definition

Amount before accumulated depreciation of tangible personal property used to produce goods and services, including, but is not limited to, tools, dies and molds, computer and office equipment.

+ References

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- References

No definition available.

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Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

+ References

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