Financial Instruments, Guarantees With Off-Balance-Sheet Risk and Other Guarantees (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Apr. 03, 2017
Guarantee Obligations [Line Items]
Letters of credit outstanding, amount	$ 437,600,000
Asset retirement obligations	728,200,000	$ 752,300,000	$ 750,200,000
Surety bonds and bank guarantees outstanding to secure reclamation obligations or activities	1,451,900,000	1,401,700,000
Letters of credit outstanding for reclamation	315,000,000.0
Line of credit facility, remaining borrowing capacity	200,000
Interest expense	139,800,000	144,200,000	151,300,000
Provision for North Goonyella equipment loss	0	83,200,000	66,400,000
Obligations
Guarantee Obligations [Line Items]
Restricted cash collateral	323,100,000	323,100,000
Accounts Receivable Securitization Program, April 3, 2020
Guarantee Obligations [Line Items]
Exit facility, maximum borrowing capacity				$ 250,000,000.0
Line of credit facility, remaining borrowing capacity	19,300,000
Surety Bond
Guarantee Obligations [Line Items]
Debt principal amount	1,633,600,000
Secured Debt | Accounts Receivable Securitization Program, April 3, 2020
Guarantee Obligations [Line Items]
Letters of credit outstanding, amount	112,300,000
Long-term debt	0
Cash collateral required	0
Interest expense	$ 2,600,000	3,300,000	5,200,000
Secured Debt | Accounts Receivable Securitization Program, April 3, 2020 | LIBOR
Guarantee Obligations [Line Items]
Basis spread on variable rate	1.50%
Australian Mining
Guarantee Obligations [Line Items]
Provision for North Goonyella equipment loss		$ 300,000	$ 50,400,000