Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2021

Accounting Policies [Abstract]

Property, Plant and Equipment

The estimated useful lives by category of assets are as follows:

	Years
Building and improvements	up to 29
Machinery and equipment	1 - 15
Leasehold improvements	Shorter of Useful Life or Remaining Life of Lease

Property, plant, equipment and mine development, net, as of December 31, 2021 and December 31, 2020 consisted of the following:

	December 31,
	2021		2020
	(Dollars in millions)
Land and coal interests	$	2,494.1	$	2,482.9
Buildings and improvements	550.8		481.0
Machinery and equipment	1,386.5		1,408.5
Less: Accumulated depreciation, depletion and amortization	(1,480.5)		(1,321.3)
Property, plant, equipment and mine development, net	$	2,950.6	$	3,051.1