Long-term Debt - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended					9 Months Ended		42 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Oct. 01, 2018	Aug. 09, 2018	Dec. 31, 2017	Sep. 18, 2017	Apr. 03, 2017	Feb. 15, 2017
Debt Instrument [Line Items]
Debt issuance cost	$ 46,100,000	$ 46,100,000		$ 55,500,000			$ 46,100,000		$ 46,100,000
Interest expense		34,900,000			$ 35,400,000		102,300,000	$ 107,200,000
Repayments of lines of credit							70,000,000.0
Letters of credit outstanding, amount	$ 334,800,000	$ 334,800,000					$ 334,800,000		$ 334,800,000
Successor Credit Agreement
Debt Instrument [Line Items]
Debt instrument, covenant, fixed charge coverage ratio							2.25
Senior Notes | 6.000% Senior Secured Notes due March 2022
Debt Instrument [Line Items]
Stated interest rate	6.00%	6.00%					6.00%		6.00%
Debt instrument, restricted payments, amount paid											$ 10.00
Debt instrument, restricted payments, principal amount used to calculate payments											1,000
Debt instrument, repurchase amount				41,000,000.0
Debt instrument repurchase amount, excluding interest				39,900,000
Write off of deferred debt issuance cost				1,300,000
Gain (loss) on extinguishment of debt				200,000
Long-term debt	$ 459,000,000.0	$ 459,000,000.0		459,000,000.0			$ 459,000,000.0		$ 459,000,000.0
Senior Notes | 6.000% Senior Secured Notes due March 2022 | Debt Instrument, Redemption, Period One
Debt Instrument [Line Items]
Redemption price, percentage							103.00%
Senior Notes | 6.000% Senior Secured Notes due March 2022 | Debt Instrument, Redemption, Period Two
Debt Instrument [Line Items]
Redemption price, percentage							101.50%
Senior Notes | 6.000% Senior Secured Notes due March 2022 | Effect of Plan
Debt Instrument [Line Items]
Principal amount															$ 500,000,000.0
Stated interest rate															6.00%
Senior Notes | 6.375% Senior Secured Notes due March 2025
Debt Instrument [Line Items]
Stated interest rate	6.375%	6.375%					6.375%		6.375%
Debt instrument, restricted payments, amount paid											30.00
Debt instrument, restricted payments, principal amount used to calculate payments											1,000
Long-term debt	$ 500,000,000.0	$ 500,000,000.0		500,000,000.0			$ 500,000,000.0		$ 500,000,000.0
Senior Notes | 6.375% Senior Secured Notes due March 2025 | Debt Instrument, Redemption, Period One
Debt Instrument [Line Items]
Redemption price, percentage							104.80%
Senior Notes | 6.375% Senior Secured Notes due March 2025 | Debt Instrument, Redemption, Period Two
Debt Instrument [Line Items]
Redemption price, percentage							103.20%
Senior Notes | 6.375% Senior Secured Notes due March 2025 | Debt Instrument, Redemption, Period Three
Debt Instrument [Line Items]
Redemption price, percentage							101.60%
Senior Notes | 6.375% Senior Secured Notes due March 2025 | Effect of Plan
Debt Instrument [Line Items]
Principal amount															$ 500,000,000.0
Stated interest rate															6.375%
Senior Notes | 6.00% And 6.375% Senior Secured Notes, Successor Notes
Debt Instrument [Line Items]
Debt issuance cost															$ 49,500,000
Interest expense		$ 17,500,000			18,100,000		$ 52,500,000	54,200,000
Senior Notes | 6.00% And 6.375% Senior Secured Notes, Successor Notes | Domestic
Debt Instrument [Line Items]
Collateral, capital stock, percent	100.00%	100.00%					100.00%		100.00%
Senior Notes | 6.00% And 6.375% Senior Secured Notes, Successor Notes | Export
Debt Instrument [Line Items]
Collateral, non-voting capital stock, percent	100.00%	100.00%					100.00%		100.00%
Collateral, voting capital stock, percent	65.00%	65.00%					65.00%		65.00%
Senior Notes | 6.00% And 6.375% Senior Secured Notes, Successor Notes | Peabody Investments (Gibraltar) Limited
Debt Instrument [Line Items]
Collateral, non-voting capital stock, percent	100.00%	100.00%					100.00%		100.00%
Collateral, voting capital stock, percent	65.00%	65.00%					65.00%		65.00%
Senior Notes | Successor Credit Agreement
Debt Instrument [Line Items]
Debt instrument, restricted payments basket											650,000,000.0
Debt instrument, restricted payments basket											150,000,000.0
Aggregate consent payments											$ 19,800,000
Term Loan | Successor Credit Agreement
Debt Instrument [Line Items]
Principal amount	$ 400,000,000.0	$ 400,000,000.0					$ 400,000,000.0		$ 400,000,000.0
Interest expense		$ 3,400,000			5,600,000		12,100,000	17,000,000.0
Debt instrument, restricted payments basket													$ 450,000,000.0
Original issue discount and deferred finance costs														$ 37,300,000
Debt instrument, periodic payment							$ 1,000,000.0
Debt instrument, principal prepayment, percent of principal amount if repaid before October 2018										101.00%
Mandatory principal prepayment, percent of excess cash flow	75.00%	75.00%					75.00%		75.00%
Mandatory principal prepayment, if required, period payable, threshold							100 days
Excess proceeds from sales of assets, threshold ($10 million or greater)	$ 10,000,000.0	$ 10,000,000.0					$ 10,000,000.0		$ 10,000,000.0
Repayments of debt						$ 46,000,000.0			560,000,000.0
Payment for debt extinguishment or debt prepayment cost									546,000,000.0
Restricted payments threshold	$ 450,000,000.0	$ 450,000,000.0					$ 450,000,000.0		$ 450,000,000.0				50,000,000.0
Debt instrument, covenant, fixed charge coverage ratio							2.00
Debt instrument, floor interest rate	1.00%	1.00%					1.00%		1.00%
Debt instrument, extended term							3 years
Term Loan | Successor Credit Agreement | Total Leverage Ratio Less or Equal to 2.00 to 1.00 Greater Than 1.50 to 1.00
Debt Instrument [Line Items]
Mandatory principal prepayment, percent of excess cash flow	50.00%	50.00%					50.00%		50.00%
Term Loan | Successor Credit Agreement | Total Leverage Ratio Less or Equal to 2.00 to 1.00 Greater Than 1.50 to 1.00 | Maximum
Debt Instrument [Line Items]
Total leverage ratio	2.00	2.00					2.00		2.00
Term Loan | Successor Credit Agreement | Total Leverage Ratio Less or Equal to 2.00 to 1.00 Greater Than 1.50 to 1.00 | Minimum
Debt Instrument [Line Items]
Total leverage ratio	1.50	1.50					1.50		1.50
Term Loan | Successor Credit Agreement | Total Leverage Ratio Less or Equal to 1.50 to 1.00 Greater Than 1.00 to 1.00
Debt Instrument [Line Items]
Mandatory principal prepayment, percent of excess cash flow	25.00%	25.00%					25.00%		25.00%
Term Loan | Successor Credit Agreement | Total Leverage Ratio Less or Equal to 1.50 to 1.00 Greater Than 1.00 to 1.00 | Maximum
Debt Instrument [Line Items]
Total leverage ratio	1.50	1.50					1.50		1.50
Term Loan | Successor Credit Agreement | Total Leverage Ratio Less or Equal to 1.50 to 1.00 Greater Than 1.00 to 1.00 | Minimum
Debt Instrument [Line Items]
Total leverage ratio	1.00	1.00					1.00		1.00
Term Loan | Successor Credit Agreement | Total Leverage Ratio Less or Equal to 1.00 to 1.00
Debt Instrument [Line Items]
Mandatory principal prepayment, percent of excess cash flow	0.00%	0.00%					0.00%		0.00%
Total leverage ratio	1.00	1.00					1.00		1.00
Term Loan | Successor Credit Agreement | Total Leverage Ration Less Or Equal 2.00 to 1.00
Debt Instrument [Line Items]
Total leverage ratio	2.00	2.00					2.00		2.00
Term Loan | Successor Credit Agreement | Total Leverage Ratio Less or Equal 1.25 to 1.00
Debt Instrument [Line Items]
Total leverage ratio	1.25	1.25					1.25		1.25
Dividend payment and stock purchase payment threshold	$ 25,000,000.0	$ 25,000,000.0					$ 25,000,000.0		$ 25,000,000.0
Term Loan | Successor Credit Agreement | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate							2.75%
Term Loan | Successor Credit Agreement | Effect of Plan
Debt Instrument [Line Items]
Principal amount														950,000,000.0
Term Loan | Senior Secured Term Loan due 2025, net of original issue discount
Debt Instrument [Line Items]
Secured debt														$ 950,000,000.0
Long-term debt	389,200,000	389,200,000		392,100,000			$ 389,200,000		389,200,000
Line of credit | Revolving Credit Facility
Debt Instrument [Line Items]
Long-term debt	230,000,000.0	230,000,000.0		0			230,000,000.0		230,000,000.0
Revolving credit facility availability	5,100,000	5,100,000		498,600,000			5,100,000		5,100,000
Line of credit | 2017 Revolver | Revolving Credit Facility
Debt Instrument [Line Items]
Long-term debt													$ 350,000,000.0
Revolving Credit Facility | 2017 Revolver
Debt Instrument [Line Items]
Debt issuance cost	5,700,000	5,700,000					5,700,000		5,700,000			$ 4,700,000
Interest expense		5,100,000			1,400,000		10,800,000	4,500,000
Line of credit facility, maximum borrowing capacity	565,000,000.0	565,000,000.0					565,000,000.0		565,000,000.0			$ 350,000,000.0
2019 Revolver commitments, matures 2023	540,000,000.0	540,000,000.0					540,000,000.0		540,000,000.0
2019 Revolver commitments, matures 2020	25,000,000.0	25,000,000.0					25,000,000.0		25,000,000.0
Unrestricted cash netting limit							800,000,000.0
Proceeds from lines of credit			$ 300,000,000.0
Repayments of lines of credit		70,000,000.0
Letters of credit outstanding, amount	329,900,000	329,900,000					329,900,000		329,900,000
Revolving credit facility availability	$ 5,100,000	$ 5,100,000					$ 5,100,000		$ 5,100,000
Revolving credit facility, fee on unused borrowings	0.40%	0.40%					0.40%		0.40%
Debt instrument, base interest rate	3.125%	3.125%					3.125%		3.125%
Revolving Credit Facility | 2017 Revolver | Total Leverage Ration Less Or Equal 2.00 to 1.00
Debt Instrument [Line Items]
Total leverage ratio	2.00	2.00					2.00		2.00
Revolving Credit Facility | 2017 Revolver | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate							3.00%
Secured debt | Accounts Receivable Securitization Program, April 1, 2022
Debt Instrument [Line Items]
Interest expense		$ 800,000			$ 1,000,000.0		$ 2,900,000	$ 3,600,000
Long-term debt	$ 60,000,000.0	60,000,000.0		$ 0			60,000,000.0		$ 60,000,000.0
Line of credit facility, maximum borrowing capacity	250,000,000.0	250,000,000.0					250,000,000.0		250,000,000.0
Letters of credit outstanding, amount	3,400,000	$ 3,400,000					$ 3,400,000		$ 3,400,000
Amount borrowed from accounts receivable securitization	$ 60,000,000.0
Secured debt | Accounts Receivable Securitization Program, April 1, 2022 | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate	1.50%