Emergence from the Chapter 11 Cases and Fresh Start Reporting - Effect of Reorganization Plan and Fresh Start Adjustments on Balance Sheet (Details)	Apr. 01, 2017 USD ($)
Fresh-Start Adjustment, Increase (Decrease), Assets [Abstract]
Fresh-start adjustment, increase (decrease), restricted cash	$ 1,000,000,000
Fresh-Start Adjustment, Increase (Decrease), Liabilities [Abstract]
Fresh-start adjustment, increase (decrease), long-term debt, less current portion	950,000,000
Fresh-Start Adjustment, Increase (Decrease), Stockholders' Equity [Abstract]
Fresh-start adjustment, increase (decrease), Series A preferred stock	1,305,400,000
Net impact on accumulated deficit	5,134,300,000
Effect of Plan
Fresh-Start Adjustment, Increase (Decrease), Assets [Abstract]
Fresh-start adjustment, increase (decrease), cash and cash equivalents	(14,400,000)
Fresh-start adjustment, increase (decrease), accounts receivable, net	0
Fresh-start adjustment, increase (decrease), inventories	0
Fresh-start adjustment, increase (decrease), assets from coal trading activities, net	0
Fresh-start adjustment, increase (decrease), other current assets	(18,100,000)
Fresh-start adjustment, increase (decrease), total current assets	(1,087,200,000)
Fresh-start adjustment, increase (decrease), property, plant, equipment and mine development, net	0
Fresh-start adjustment, increase (decrease), Investments	3,900,000
Fresh-start adjustment, increase (decrease), total assets	(1,083,300,000)
Fresh-Start Adjustment, Increase (Decrease), Liabilities [Abstract]
Fresh-start adjustment, increase (decrease), current portion of long-term debt	9,500,000
Fresh-start adjustment, increase (decrease), liabilities from coal trading activities, net	0
Fresh-start adjustment, increase (decrease), accounts payable and accrued expenses	257,600,000
Fresh-start adjustment, increase (decrease), total current liabilities	267,100,000
Fresh-start adjustment, increase (decrease), long-term debt, less current portion	903,200,000
Fresh-start adjustment, increase (decrease), deferred income taxes	0
Fresh-start adjustment, increase (decrease), asset retirement obligations	0
Fresh-start adjustment, increase (decrease), accrued postretirement benefit costs	0
Fresh-start adjustment, increase (decrease), other noncurrent liabilities	0
Fresh-start adjustment, increase (decrease), total liabilities not subject to compromise	1,170,300,000
Fresh-start adjustment, increase (decrease), liabilities subject to compromise	(8,416,700,000)
Fresh-start adjustment, increase (decrease), total liabilities	(7,246,400,000)
Fresh-Start Adjustment, Increase (Decrease), Stockholders' Equity [Abstract]
Cancellation of Predecessor Treasury stock	371,900,000
Net impact on accumulated deficit	5,134,300,000
Fresh-start adjustment, increase (decrease), Peabody Energy Corporation stockholders' equity	6,163,100,000
Fresh-start adjustment, increase (decrease), noncontrolling interests	0
Fresh-start adjustment, increase (decrease), total stockholders' equity	6,163,100,000
Fresh-start adjustment, increase (decrease), liabilities and stockholders' equity	(1,083,300,000)
Fresh Start Adjustments
Fresh-Start Adjustment, Increase (Decrease), Assets [Abstract]
Fresh-start adjustment, increase (decrease), cash and cash equivalents	0
Fresh-start adjustment, increase (decrease), accounts receivable, net	0
Fresh-start adjustment, increase (decrease), inventories	70,100,000
Fresh-start adjustment, increase (decrease), assets from coal trading activities, net	0
Fresh-start adjustment, increase (decrease), other current assets	(333,000,000)
Fresh-start adjustment, increase (decrease), total current assets	(262,900,000)
Fresh-start adjustment, increase (decrease), property, plant, equipment and mine development, net	(3,461,400,000)
Fresh-start adjustment, increase (decrease), Investments	238,000,000
Fresh-start adjustment, increase (decrease), total assets	(3,486,300,000)
Fresh-Start Adjustment, Increase (Decrease), Liabilities [Abstract]
Fresh-start adjustment, increase (decrease), current portion of long-term debt	0
Fresh-start adjustment, increase (decrease), liabilities from coal trading activities, net	0
Fresh-start adjustment, increase (decrease), accounts payable and accrued expenses	14,800,000
Fresh-start adjustment, increase (decrease), total current liabilities	14,800,000
Fresh-start adjustment, increase (decrease), long-term debt, less current portion	0
Fresh-start adjustment, increase (decrease), deferred income taxes	(177,800,000)
Fresh-start adjustment, increase (decrease), asset retirement obligations	(73,900,000)
Fresh-start adjustment, increase (decrease), accrued postretirement benefit costs	(6,900,000)
Fresh-start adjustment, increase (decrease), other noncurrent liabilities	120,600,000
Fresh-start adjustment, increase (decrease), total liabilities not subject to compromise	(123,200,000)
Fresh-start adjustment, increase (decrease), liabilities subject to compromise	0
Fresh-start adjustment, increase (decrease), total liabilities	(123,200,000)
Fresh-Start Adjustment, Increase (Decrease), Stockholders' Equity [Abstract]
Net impact on accumulated deficit	(3,850,200,000)
Fresh-start adjustment, increase (decrease), accumulated other comprehensive loss	448,500,000
Fresh-start adjustment, increase (decrease), Peabody Energy Corporation stockholders' equity	(3,401,700,000)
Fresh-start adjustment, increase (decrease), noncontrolling interests	38,600,000
Fresh-start adjustment, increase (decrease), total stockholders' equity	(3,363,100,000)
Fresh-start adjustment, increase (decrease), liabilities and stockholders' equity	(3,486,300,000)
Predecessor
Preconfirmation, Current Assets [Abstract]
Preconfirmation, cash and cash equivalents	1,068,100,000
Preconfirmation, accounts receivable, net	312,100,000
Preconfirmation, inventories	250,800,000
Preconfirmation, assets from coal trading activities, net	600,000
Preconfirmation, other current assets	493,900,000
Preconfirmation, total current assets	3,206,200,000
Preconfirmation, property, plant, equipment and mine development, net	8,653,900,000
Preconfirmation, investments and orher assets	976,400,000
Preconfirmation, total assets	12,836,500,000
Preconfirmation, Current Liabilities [Abstract]
Preconfirmation, current portion of long-term debt	18,200,000
Preconfirmation, liabilities from coal trading activities, net	700,000
Preconfirmation, accounts payable and accrued expenses	967,300,000
Preconfirmation, total current liabilities	986,200,000
Preconfirmation, long-term debt, less current portion	950,500,000
Preconfirmation, deferred income taxes	179,200,000
Preconfirmation, asset retirement obligations	707,000,000
Preconfirmation, accrued postretirement benefit costs	753,900,000
Preconfirmation, other noncurrent liabilities	511,100,000
Preconfirmation, total liabilities not subject to compromise	4,087,900,000
Preconfirmation, liabilities subject to compromise	8,416,700,000
Preconfirmation, total liabilities	12,504,600,000
Preconfirmation, Stockholders' Equity [Abstract]
Preconfirmation, common stock	200,000
Preconfirmation, additional paid-in capital	2,423,900,000
Preconfirmation, treasury stock, at cost	(371,900,000)
Preconfirmation, accumulated deficit	(1,284,100,000)
Preconfirmation, accumulated other comprehensive loss	(448,500,000)
Preconfirmation, Peabody Energy Corporation stockholders' equity	319,600,000
Preconfirmation, noncontrolling interests	12,300,000
Preconfirmation, total stockholders' equity	331,900,000
Preconfirmation, total liabilities and stockholders' equity	12,836,500,000
Fresh-Start Adjustment, Increase (Decrease), Stockholders' Equity [Abstract]
Successor Common Stock	200,000
Successor Additional paid-in capital	2,423,900,000
Cancellation of Predecessor Treasury stock	(371,900,000)
Predecessor | Effect of Plan
Fresh-Start Adjustment, Increase (Decrease), Stockholders' Equity [Abstract]
Successor Common Stock	(200,000)
Successor Additional paid-in capital	(2,423,900,000)
Successor
Fresh-Start Adjustment, Increase (Decrease), Stockholders' Equity [Abstract]
Successor Common Stock	700,000
Successor Additional paid-in capital	1,774,900,000
Postconfirmation, Current Assets [Abstract]
Postconfirmation, cash and cash equivalents	1,053,700,000
Postconfirmation, accounts receivable, net	312,100,000
Postconfirmation, inventories	320,900,000
Postconfirmation, assets from coal trading activities	600,000
Postconfirmation, other current assets	142,800,000
Postconfirmation, total current assets	1,856,100,000
Postconfirmation, property, plant, equipment and mine development, net	5,192,500,000
Postconfirmation, investments and orher assets	1,218,300,000
Postconfirmation, total assets	8,266,900,000
Postconfirmation, current portion of long-term debt	27,700,000
Postconfirmation, liabilities from coal trading activities, net	700,000
Postconfirmation, accounts payable and accrued expenses	1,239,700,000
Postconfirmation, total current liabilities	1,268,100,000
Postconfirmation, long-term debt, less current portion	1,853,700,000
Postconfirmation, deferred income taxes	1,400,000
Postconfirmation, asset retirement obligations	633,100,000
Postconfirmation, accrued postretirement benefit costs	747,000,000
Postconfirmation, other noncurrent liabilities	631,700,000
Postconfirmation, total liabilities not subject to compromise	5,135,000,000
Postconfirmation, liabilities subject to compromise	0
Postconfirmation, total liabilities	5,135,000,000
Postconfirmation, common stock	700,000
Postconfirmation, Series A preferred stock	1,305,400,000
Postconfirmation, additional paid-in capital	1,774,900,000
Postconfirmation, treasury stock, at cost	0
Postconfirmation, accumulated deficit	0
Postconfirmation, accumulated other comprehensive loss	0
Postconfirmation, noncontrolling interests	50,900,000
Postconfirmation, total stockholders' equity	3,131,900,000
Postconfirmation, total liabilities and stockholders' equity	8,266,900,000
Successor | Effect of Plan
Fresh-Start Adjustment, Increase (Decrease), Stockholders' Equity [Abstract]
Successor Common Stock	700,000
Fresh-start adjustment, increase (decrease), Series A preferred stock	1,305,400,000
Successor Additional paid-in capital	1,774,900,000
Postconfirmation, Current Assets [Abstract]
Postconfirmation, Series A preferred stock	750,000,000
Postconfirmation, Peabody Energy Corporation stockholders' equity	3,081,000,000
Postconfirmation, total stockholders' equity	3,105,000,000
Successor | Fresh Start Adjustments
Fresh-Start Adjustment, Increase (Decrease), Stockholders' Equity [Abstract]
Successor Common Stock	0
Fresh-start adjustment, increase (decrease), Series A preferred stock	0
Successor Additional paid-in capital	0
Cancellation of Predecessor Treasury stock	0
Restricted Cash Other Than Proceeds from Successor Notes | Effect of Plan
Fresh-Start Adjustment, Increase (Decrease), Assets [Abstract]
Fresh-start adjustment, increase (decrease), restricted cash	(54,700,000)
Restricted Cash Other Than Proceeds from Successor Notes | Fresh Start Adjustments
Fresh-Start Adjustment, Increase (Decrease), Assets [Abstract]
Fresh-start adjustment, increase (decrease), restricted cash	0
Restricted Cash Other Than Proceeds from Successor Notes | Predecessor
Preconfirmation, Current Assets [Abstract]
Preconfirmation, restricted cash	80,700,000
Restricted Cash Other Than Proceeds from Successor Notes | Successor
Postconfirmation, Current Assets [Abstract]
Postconfirmation, restricted cash	26,000,000
Proceeds from Successor Notes | Effect of Plan
Fresh-Start Adjustment, Increase (Decrease), Assets [Abstract]
Fresh-start adjustment, increase (decrease), restricted cash	(1,000,000,000)
Proceeds from Successor Notes | Fresh Start Adjustments
Fresh-Start Adjustment, Increase (Decrease), Assets [Abstract]
Fresh-start adjustment, increase (decrease), restricted cash	0
Proceeds from Successor Notes | Predecessor
Preconfirmation, Current Assets [Abstract]
Preconfirmation, restricted cash	1,000,000,000
Proceeds from Successor Notes | Successor
Postconfirmation, Current Assets [Abstract]
Postconfirmation, restricted cash	0
Senior Notes | 7.875% Senior Notes due November 2026 | Effect of Plan
Fresh-Start Adjustment, Increase (Decrease), Liabilities [Abstract]
Fresh-start adjustment, increase (decrease), long-term debt, less current portion	(250,000,000.0)
Senior Notes | 10.00% Senior Secured Second Lien Notes due March 2022 | Effect of Plan
Fresh-Start Adjustment, Increase (Decrease), Liabilities [Abstract]
Fresh-start adjustment, increase (decrease), long-term debt, less current portion	(1,000,000,000.0)
Senior Notes | 6.50% Senior Notes due September 2020 | Effect of Plan
Fresh-Start Adjustment, Increase (Decrease), Liabilities [Abstract]
Fresh-start adjustment, increase (decrease), long-term debt, less current portion	(650,000,000.0)
Subordinated Debt | Convertible Junior Subordinated Debentures due December 2066 | Effect of Plan
Fresh-Start Adjustment, Increase (Decrease), Liabilities [Abstract]
Fresh-start adjustment, increase (decrease), long-term debt, less current portion	$ (732,500,000.0)