Management - Labor Relations (Details)	12 Months Ended
	Dec. 31, 2021 numberOfEmployee numberOfMine
Concentration Risk [Line Items]
Number of employees	4,900
Number of hourly employees	3,900
Hourly employees represented by organized labor unions (in percent)	34.00%
Coal production generated by hourly employees represented by organized labor unions (in percent)	16.00%
Number of us mines represented by unions | numberOfMine	1
Represented by Organized Labor Union | Kayenta Mine
Concentration Risk [Line Items]
Number of employees	15
Represented by Organized Labor Union | Shoal Creek
Concentration Risk [Line Items]
Number of employees	280
Represented by Organized Labor Union | Wilpinjong Mine
Concentration Risk [Line Items]
Number of employees	480
Represented by Organized Labor Union | Coppabella Mine
Concentration Risk [Line Items]
Number of employees	280
Represented by Organized Labor Union | Moorvale Mine
Concentration Risk [Line Items]
Number of employees	150
Represented by Organized Labor Union | Metropolitan Underground Mine
Concentration Risk [Line Items]
Number of employees	145
Represented by Organized Labor Union | Metropolitan Prep Plant
Concentration Risk [Line Items]
Number of employees	20
Represented by Organized Labor Union | Wambo Underground Mine
Concentration Risk [Line Items]
Number of employees	75
Represented by Organized Labor Union | Wambo Prep Plant
Concentration Risk [Line Items]
Number of employees	20