Financial Instruments and Other Guarantees (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Guarantee Obligations [Line Items]
Letters of credit outstanding, amount	$ 423,400,000
Surety bonds amount	1,570,800,000
Asset retirement obligations	735,900,000
Surety bonds issued to support asset retirement obligations	1,394,500,000
Letters of credit issued to support asset retirement obligations	297,700,000
Net interest expense	52,400,000	$ 33,100,000
Accounts Receivable Securitization Program, April 1, 2022 | Secured debt
Guarantee Obligations [Line Items]
Letters of credit outstanding, amount	120,800,000
Line of credit facility, maximum borrowing capacity	250,000,000.0
Outstanding borrowings	0
Accounts Receivable from Securitization	800,000
Collateral posted	43,500,000		$ 0
Net interest expense	$ 700,000
Secured debt | Accounts Receivable Securitization Program, April 1, 2022 | London Interbank Offered Rate (LIBOR) Swap Rate
Guarantee Obligations [Line Items]
Basis spread on variable rate	1.50%