Summary of Significant Accounting Policies Discussion (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended																			9 Months Ended	12 Months Ended
	Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015		Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Apr. 12, 2016	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Income Tax Expense (Benefit)									$ 7.9				$ 67.4							$ (22.7)	$ (94.5)	$ (207.1)	$ 147.4
(Loss) Income from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	$ (175.2)		$ (97.7)		$ (223.2)		$ (167.7)		(502.0)								$ (126.4)	$ (1,006.0)	$ (148.8)	(423.6)	(663.8)	(1,783.2)	(695.3)
Net (loss) income	(188.3)		(135.8)		(226.2)		(171.1)		(474.3)								(283.9)	(1,042.3)	(157.7)	(477.2)	(721.4)	(1,958.2)	(723.5)
Net Income (Loss) Attributable to Parent	(192.7)		$ (137.6)		(227.9)		(171.1)		(473.5)								$ (286.7)	$ (1,044.1)	$ (161.0)	(485.1)	(729.3)	(1,965.3)	(733.2)
Other current assets	486.6								447.6											486.6	$ 486.6	447.6
First Lien Exit Facility																					1.95
Other Assets, Noncurrent	910.4								363.7											910.4	$ 910.4	363.7
Total assets	11,777.7								10,946.9											11,777.7	11,777.7	10,946.9	13,191.1
Long-term Debt and Capital Lease Obligations, Current	20.2								5,874.9											20.2	20.2	5,874.9
Long-term Debt and Capital Lease Obligations	0.0								366.3											0.0	0.0	366.3
Liabilities	$ 11,596.2								10,195.2											$ 11,596.2	$ 11,596.2	$ 10,195.2
Initial Offering Period																					750
Proceeds from Issuance of Private Placement																					$ 750.0
Equity Investment necessary to consummate Reorg Plan																					1.5
Take-back Paper																					1.5
Summary Of Significant Accounting Policies Discussion Textuals [Abstract]
Stockholders' Equity, Reverse Stock Split																					Pursuant to the authorization provided at a special meeting of the Company's stockholders held on September 16, 2015, the Company completed a 1-for-15 reverse stock split of the shares of the Company’s common stock on September 30, 2015 (the Reverse Stock Split). Refer to Note 1. "Summary of Significant Accounting Policies" for additional details surrounding the Reverse Stock Split.	Pursuant to the authorization provided at a special meeting of the Company's stockholders held on September 16, 2015, the Company completed a 1-for-15 reverse stock split of the shares of the Company’s common stock on September 30, 2015 (the Reverse Stock Split). As a result of the Reverse Stock Split, every 15 shares of issued and outstanding common stock were combined into one issued and outstanding share of Common Stock, without any change in the par value per share.
Common Stock, Shares Authorized	53.3																			53.3	53.3
Common Stock, Par or Stated Value Per Share	$ 0.01																			$ 0.01	$ 0.01
Cash and cash equivalents	$ 872.3								261.3											$ 872.3	$ 872.3	$ 261.3	298.0	$ 652.1	$ 444.0
Period considered to treat short-term, highly liquid investments as cash equivalents																					three months or less
Other-than-temporary impairment losses on marketable securities																					$ 0.0	4.7	4.7
Other-than-temporary impairment losses on equity and cost method investments																					$ 276.5	0.0
Recognition of tax benefits from uncertain tax positions																					greater than fifty percent likelihood of being realized upon ultimate settlement
Restructuring charges for voluntary and involuntary workforce reductions																				2.8	$ 15.5	23.5	26.0
Asset impairment charges related to long-lived assets																					247.9	1,001.3	149.7
Foreign currency remeasurement (loss) gains																					7.4	(6.4)	(1.3)
Foreign currency translation adjustment																					1.8	34.9	41.0
Deferred Tax Liabilities, Net, Noncurrent	173.9								235.9											173.9	173.9	235.9	0.0
Retained Earnings (Accumulated Deficit)	(1,399.5)								(670.2)											(1,399.5)	(1,399.5)	(670.2)	0.0
Total stockholders' equity	$ 181.5								$ 751.7											$ 181.5	$ 181.5	$ 751.7	2,529.0		3,696.6
Buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life																					3 to 34
Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life																					3 to 34
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life																					Shorter of Useful Life or Remaining Life of Lease
Interest In Middlemount Coal Pty Limited [Member]
Summary Of Significant Accounting Policies Discussion Textuals [Abstract]
Ownership percentage of equity method investment	50.00%																			50.00%	50.00%
Minimum [Member] | Buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life																					1
Minimum [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life																					1
Maximum [Member] | Buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life																					37
Maximum [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life																					37
Common Stock [Member]
Property, Plant and Equipment [Line Items]
Stock Issued During Period, Shares, Reverse Stock Splits																					278.0
Common Stock, Shares, issues post reverse stock split	19.0																			19.0	19.0
Stock Authorized During Period, Shares, Reverse Stock Splits									800.0													800.0
Summary Of Significant Accounting Policies Discussion Textuals [Abstract]
Common Stock, Shares Authorized	53.3								53.3											53.3	53.3	53.3
Common Stock, Par or Stated Value Per Share	$ 0.01								$ 0.01											$ 0.01	$ 0.01	$ 0.01
Debt burden reduced at exit of bankruptcy [Member]
Property, Plant and Equipment [Line Items]
Long-term Debt	$ 6,600.0																			$ 6,600.0	$ 6,600.0
Revolving Credit Facility [Member]
Property, Plant and Equipment [Line Items]
Long-term Debt	1,558.1						947.0		$ 0.0											1,558.1	1,558.1	$ 0.0
Summary Of Significant Accounting Policies Discussion Textuals [Abstract]
Exit facility, maximum borrowing capacity	1,650.0																			1,650.0	1,650.0
6.50% Senior Notes due September 2020 [Member]
Property, Plant and Equipment [Line Items]
Long-term Debt	$ 645.8								645.5											$ 645.8	$ 645.8	645.5
Summary Of Significant Accounting Policies Discussion Textuals [Abstract]
Stated interest rate - percentage	6.50%		6.50%																	6.50%	6.50%
10.00% Senior Secured Second Lien Notes Due 2022 [Member]
Property, Plant and Equipment [Line Items]
Long-term Debt	$ 962.3								960.4											$ 962.3	$ 962.3	960.4
Face amount of senior notes	$ 1,000.0																			$ 1,000.0	$ 1,000.0
Summary Of Significant Accounting Policies Discussion Textuals [Abstract]
Stated interest rate - percentage	10.00%																			10.00%	10.00%
6.00% Senior Notes due November 2018 [Member]
Property, Plant and Equipment [Line Items]
Long-term Debt	$ 1,509.9								1,508.9											$ 1,509.9	$ 1,509.9	1,508.9
Summary Of Significant Accounting Policies Discussion Textuals [Abstract]
Stated interest rate - percentage	6.00%																			6.00%	6.00%
6.25% Senior Notes due November 2021 [Member]
Property, Plant and Equipment [Line Items]
Long-term Debt	$ 1,327.7								1,327.0											$ 1,327.7	$ 1,327.7	1,327.0
Summary Of Significant Accounting Policies Discussion Textuals [Abstract]
Stated interest rate - percentage	6.25%		6.25%																	6.25%	6.25%
7.875% Senior Notes [Member]
Summary Of Significant Accounting Policies Discussion Textuals [Abstract]
Stated interest rate - percentage	7.875%																			7.875%	7.875%
Term Loan Facility [Member]
Summary Of Significant Accounting Policies Discussion Textuals [Abstract]
Stated interest rate - percentage	4.50%																			4.50%	4.50%
Exit facility, maximum borrowing capacity	$ 950.0																			$ 950.0	$ 950.0
6.000% Senior Secured Notes Due 2022 [Member]
Property, Plant and Equipment [Line Items]
Face amount of senior notes	$ 500.0																			$ 500.0	$ 500.0
Summary Of Significant Accounting Policies Discussion Textuals [Abstract]
Stated interest rate - percentage	6.00%																			6.00%	6.00%
6.375% Senior Secured Notes Due 2022 [Member]
Property, Plant and Equipment [Line Items]
Face amount of senior notes	$ 500.0																			$ 500.0	$ 500.0
Summary Of Significant Accounting Policies Discussion Textuals [Abstract]
Stated interest rate - percentage	6.375%																			6.375%	6.375%
Scenario, Previously Reported [Member]
Property, Plant and Equipment [Line Items]
Income Tax Expense (Benefit)																					$ (84.0)	(176.4)	201.2
(Loss) Income from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	$ (186.2)		$ (95.6)		(230.8)		(161.7)		(497.9)		$ (144.4)		(1,007.2)		$ (164.4)						(674.3)	(1,813.9)	(749.1)
Net (loss) income	(199.3)		(133.7)		(233.8)		(165.1)		(470.2)		(301.9)		(1,043.5)		(173.3)						(731.9)	(1,988.9)	(777.3)
Net Income (Loss) Attributable to Parent	$ (203.7)		$ (135.5)		$ (235.5)		$ (165.1)		$ (469.4)		$ (304.7)		$ (1,045.3)		$ (176.6)						$ (739.8)	$ (1,996.0)	$ (787.0)
Summary Of Significant Accounting Policies Discussion Textuals [Abstract]
Income (Loss) from Continuing Operations, Per Basic and Diluted Share	$ (10.42)	[1]	$ (5.32)	[1]	$ (12.71)	[1]	$ (8.85)	[1]	$ (27.28)	[2]	$ (8.08)	[2]	$ (55.59)	[2]	$ (9.31)	[2]					$ (37.30)	$ (100.34)	$ (42.52)
Deferred Tax Liabilities, Net, Noncurrent	$ 0.0								$ 0.0											$ 0.0	$ 0.0	$ 0.0	$ 0.0
Retained Earnings (Accumulated Deficit)	0.0								0.0											0.0	0.0	0.0	$ 0.0
Paid to second lien noteholders in partial satisfaction of their claims [Member]
Property, Plant and Equipment [Line Items]
Cash	450.0																			450.0	$ 450.0
Second Lien Notes																					450
First Lien Debtholders [Member]
Property, Plant and Equipment [Line Items]
First Lien Debt																					450
Class 5B Claims [Member]
Property, Plant and Equipment [Line Items]
Pro Rate Share in Cash	75.0																			75.0	$ 75.0
Class 5A Claims [Member]
Property, Plant and Equipment [Line Items]
Cash	5.0																			5.0	$ 5.0
Eurocurrency Rate [Member] | Term Loan Facility [Member]
Property, Plant and Equipment [Line Items]
Debt instrument, basis spread on variable rate																					1.00%
Non-Debtor Subsidiaries [Member]
Property, Plant and Equipment [Line Items]
Income Tax Expense (Benefit)																				(2.1)
(Loss) Income from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest																				(207.6)
Net (loss) income																				(201.7)
Net Income (Loss) Attributable to Parent																				(209.6)
Other current assets	416.2																			416.2	$ 416.2
Lease Commitments																					189
Other Assets, Noncurrent	596.7																			596.7	$ 596.7
Total assets	6,012.9																			6,012.9	6,012.9
Long-term Debt and Capital Lease Obligations, Current	0.9																			0.9	0.9
Liabilities	2,199.0																			2,199.0	2,199.0
Summary Of Significant Accounting Policies Discussion Textuals [Abstract]
Cash and cash equivalents	477.8																			477.8	477.8			$ 543.6
Restructuring charges for voluntary and involuntary workforce reductions																				0.6
Deferred Tax Liabilities, Net, Noncurrent	161.8																			161.8	161.8
Total stockholders' equity	3,813.9																			3,813.9	3,813.9
Other Current Assets [Member]
Property, Plant and Equipment [Line Items]
Deferred Finance Costs, Current	(55.5)																			(55.5)	(55.5)
Other Noncurrent Assets [Member]
Property, Plant and Equipment [Line Items]
Deferred Finance Costs, Current	(18.9)																			(18.9)	(18.9)
Assets [Member]
Property, Plant and Equipment [Line Items]
Deferred Finance Costs, Current	(74.4)																			(74.4)	(74.4)
Long-term Debt and Capital Lease Obligations, Current [Member]
Property, Plant and Equipment [Line Items]
Deferred Finance Costs, Current	(55.5)																			(55.5)	(55.5)
Long-term Debt and Capital Lease Obligations [Member]
Property, Plant and Equipment [Line Items]
Deferred Finance Costs, Current	(18.9)																			(18.9)	(18.9)
Liability [Member]
Property, Plant and Equipment [Line Items]
Deferred Finance Costs, Current	(74.4)																			(74.4)	(74.4)
Peabody Energy [Member]
Property, Plant and Equipment [Line Items]
Other current assets									503.1													503.1
Other Assets, Noncurrent									382.6													382.6
Total assets									11,021.3													11,021.3
Long-term Debt and Capital Lease Obligations, Current									5,930.4													5,930.4
Long-term Debt and Capital Lease Obligations									385.2													385.2
Liabilities									10,269.6													10,269.6
Incorrect Use of Deferred Tax Liabilities in Assessment of Valuation Allowances in 2013
Property, Plant and Equipment [Line Items]
Deferred Income Tax Liabilities, Net	$ 156.3								$ 166.8											$ 156.3	$ 156.3	$ 166.8
Incorrect Utilization [Member]
Property, Plant and Equipment [Line Items]
Deferred Income Tax Liabilities, Net																									$ 251.3

[1] EPS for the quarters may not sum to the amounts for the year as each period is computed on a discrete basis.

[2] EPS for the quarters may not sum to the amounts for the year as each period is computed on a discrete basis.