Effect of Reorganization Plan and Fresh Start Adjustments on Balance Sheet (Details) $ in Millions	Apr. 01, 2017 USD ($)
Fresh-Start Adjustment, Increase (Decrease), Assets [Abstract]
Fresh-start adjustment, increase (decrease), restricted cash	$ 1,000.0
Fresh-Start Adjustment, Increase (Decrease), Liabilities [Abstract]
Fresh-Start Adjustment, Increase (Decrease), Long-term Debt	950.0
Fresh-Start Adjustment, Increase (Decrease), Stockholders' Equity [Abstract]
Fresh-start adjustment, increase (decrease), Series A preferred stock	1,305.4
Net impact on accumulated deficit	5,134.3
Effect of Plan
Fresh-Start Adjustment, Increase (Decrease), Assets [Abstract]
Fresh-start adjustment, increase (decrease), cash and cash equivalents	(14.4)
Fresh-start adjustment, increase (decrease), accounts receivable, net	0.0
Fresh-start adjustment, increase (decrease), inventories	0.0
Fresh-start adjustment, increase (decrease), other current assets	(18.1)
Fresh-start adjustment, increase (decrease), total current assets	(1,087.2)
Fresh-start adjustment, increase (decrease), property, plant, equipment and mine development, net	0.0
Fresh-start adjustment, increase (decrease), Investments	3.9
Fresh-start adjustment, increase (decrease), total assets	(1,083.3)
Fresh-Start Adjustment, Increase (Decrease), Liabilities [Abstract]
Fresh-start adjustment, increase (decrease), current portion of long-term debt	9.5
Fresh-start adjustment, increase (decrease), accounts payable and accrued expenses	257.6
Fresh-start adjustment, increase (decrease), total current liabilities	267.1
Fresh-Start Adjustment, Increase (Decrease), Long-term Debt	903.2
Fresh-start adjustment, increase (decrease), deferred income taxes	0.0
Fresh-start adjustment, increase (decrease), asset retirement obligations	0.0
Fresh-start adjustment, increase (decrease), accrued postretirement benefit costs	0.0
Fresh-start adjustment, increase (decrease), other noncurrent liabilities	0.0
Fresh-start adjustment, increase (decrease), total liabilities not subject to compromise	1,170.3
Fresh-start adjustment, increase (decrease), liabilities subject to compromise	(8,416.7)
Fresh-start adjustment, increase (decrease), total liabilities	(7,246.4)
Fresh-Start Adjustment, Increase (Decrease), Stockholders' Equity [Abstract]
Cancellation of Predecessor Treasury stock	371.9
Net impact on accumulated deficit	5,134.3
Fresh-start adjustment, increase (decrease), Peabody Energy Corporation stockholders' equity	6,163.1
Fresh-start adjustment, increase (decrease), noncontrolling interests	0.0
Fresh-start adjustment, increase (decrease), total stockholders' equity	6,163.1
Fresh-start adjustment, increase (decrease), liabilities and stockholders' equity	(1,083.3)
Fresh Start Adjustments
Fresh-Start Adjustment, Increase (Decrease), Assets [Abstract]
Fresh-start adjustment, increase (decrease), cash and cash equivalents	0.0
Fresh-start adjustment, increase (decrease), accounts receivable, net	0.0
Fresh-start adjustment, increase (decrease), inventories	70.1
Fresh-start adjustment, increase (decrease), other current assets	(333.0)
Fresh-start adjustment, increase (decrease), total current assets	(262.9)
Fresh-start adjustment, increase (decrease), property, plant, equipment and mine development, net	(3,461.4)
Fresh-start adjustment, increase (decrease), Investments	238.0
Fresh-start adjustment, increase (decrease), total assets	(3,486.3)
Fresh-Start Adjustment, Increase (Decrease), Liabilities [Abstract]
Fresh-start adjustment, increase (decrease), current portion of long-term debt	0.0
Fresh-start adjustment, increase (decrease), accounts payable and accrued expenses	14.8
Fresh-start adjustment, increase (decrease), total current liabilities	14.8
Fresh-Start Adjustment, Increase (Decrease), Long-term Debt	0.0
Fresh-start adjustment, increase (decrease), deferred income taxes	(177.8)
Fresh-start adjustment, increase (decrease), asset retirement obligations	(73.9)
Fresh-start adjustment, increase (decrease), accrued postretirement benefit costs	(6.9)
Fresh-start adjustment, increase (decrease), other noncurrent liabilities	120.6
Fresh-start adjustment, increase (decrease), total liabilities not subject to compromise	(123.2)
Fresh-start adjustment, increase (decrease), liabilities subject to compromise	0.0
Fresh-start adjustment, increase (decrease), total liabilities	(123.2)
Fresh-Start Adjustment, Increase (Decrease), Stockholders' Equity [Abstract]
Net impact on accumulated deficit	(3,850.2)
Fresh-start adjustment, increase (decrease), accumulated other comprehensive loss	448.5
Fresh-start adjustment, increase (decrease), Peabody Energy Corporation stockholders' equity	(3,401.7)
Fresh-start adjustment, increase (decrease), noncontrolling interests	38.6
Fresh-start adjustment, increase (decrease), total stockholders' equity	(3,363.1)
Fresh-start adjustment, increase (decrease), liabilities and stockholders' equity	(3,486.3)
Predecessor
Preconfirmation, Current Assets [Abstract]
Preconfirmation, cash and cash equivalents	1,068.1
Preconfirmation, accounts receivable, net	312.1
Preconfirmation, inventories	250.8
Preconfirmation, other current assets	494.5
Preconfirmation, total current assets	3,206.2
Preconfirmation, property, plant, equipment and mine development, net	8,653.9
Preconfirmation, investments and orher assets	976.4
Preconfirmation, total assets	12,836.5
Preconfirmation, Current Liabilities [Abstract]
Preconfirmation, current portion of long-term debt	18.2
Preconfirmation, accounts payable and accrued expenses	968.0
Preconfirmation, total current liabilities	986.2
Preconfirmation, long-term debt, less current portion	950.5
Preconfirmation, deferred income taxes	179.2
Preconfirmation, asset retirement obligations	707.0
Preconfirmation, accrued postretirement benefit costs	753.9
Preconfirmation, other noncurrent liabilities	511.1
Preconfirmation, total liabilities not subject to compromise	4,087.9
Preconfirmation, liabilities subject to compromise	8,416.7
Preconfirmation, total liabilities	12,504.6
Preconfirmation, Stockholders' Equity [Abstract]
Preconfirmation, common stock	0.2
Preconfirmation, additional paid-in capital	2,423.9
Preconfirmation, treasury stock, at cost	(371.9)
Preconfirmation, accumulated deficit	(1,284.1)
Preconfirmation, accumulated other comprehensive loss	(448.5)
Preconfirmation, Peabody Energy Corporation stockholders' equity	319.6
Preconfirmation, noncontrolling interests	12.3
Preconfirmation, total stockholders' equity	331.9
Preconfirmation, total liabilities and stockholders' equity	12,836.5
Fresh-Start Adjustment, Increase (Decrease), Stockholders' Equity [Abstract]
Successor Common Stock	0.2
Successor Additional paid-in capital	2,423.9
Cancellation of Predecessor Treasury stock	(371.9)
Predecessor | Effect of Plan
Fresh-Start Adjustment, Increase (Decrease), Stockholders' Equity [Abstract]
Successor Common Stock	(0.2)
Successor Additional paid-in capital	(2,423.9)
Successor
Fresh-Start Adjustment, Increase (Decrease), Stockholders' Equity [Abstract]
Successor Common Stock	0.7
Successor Additional paid-in capital	1,774.9
Postconfirmation, Current Assets [Abstract]
Postconfirmation, cash and cash equivalents	1,053.7
Postconfirmation, accounts receivable, net	312.1
Postconfirmation, inventories	320.9
Postconfirmation, other current assets	143.4
Postconfirmation, total current assets	1,856.1
Postconfirmation, property, plant, equipment and mine development, net	5,192.5
Postconfirmation, investments and orher assets	1,218.3
Postconfirmation, total assets	8,266.9
Postconfirmation, current portion of long-term debt	27.7
Postconfirmation, accounts payable and accrued expenses	1,240.4
Postconfirmation, total current liabilities	1,268.1
Postconfirmation, long-term debt, less current portion	1,853.7
Postconfirmation, deferred income taxes	1.4
Postconfirmation, asset retirement obligations	633.1
Postconfirmation, accrued postretirement benefit costs	747.0
Postconfirmation, other noncurrent liabilities	631.7
Postconfirmation, total liabilities not subject to compromise	5,135.0
Postconfirmation, liabilities subject to compromise	0.0
Postconfirmation, total liabilities	5,135.0
Postconfirmation, common stock	0.7
Postconfirmation, Series A preferred stock	1,305.4
Postconfirmation, additional paid-in capital	1,774.9
Postconfirmation, treasury stock, at cost	0.0
Postconfirmation, accumulated deficit	0.0
Postconfirmation, accumulated other comprehensive loss	0.0
Postconfirmation, noncontrolling interests	50.9
Postconfirmation, total stockholders' equity	3,131.9
Postconfirmation, total liabilities and stockholders' equity	8,266.9
Successor | Effect of Plan
Fresh-Start Adjustment, Increase (Decrease), Stockholders' Equity [Abstract]
Successor Common Stock	0.7
Fresh-start adjustment, increase (decrease), Series A preferred stock	1,305.4
Successor Additional paid-in capital	1,774.9
Postconfirmation, Current Assets [Abstract]
Postconfirmation, Series A preferred stock	750.0
Postconfirmation, Peabody Energy Corporation stockholders' equity	3,081.0
Postconfirmation, total stockholders' equity	3,105.0
Successor | Fresh Start Adjustments
Fresh-Start Adjustment, Increase (Decrease), Stockholders' Equity [Abstract]
Successor Common Stock	0.0
Fresh-start adjustment, increase (decrease), Series A preferred stock	0.0
Successor Additional paid-in capital	0.0
Cancellation of Predecessor Treasury stock	0.0
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	(54.7)
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	0.0
Restricted Cash Other Than Proceeds from Successor Notes | Predecessor
Preconfirmation, Current Assets [Abstract]
Preconfirmation, restricted cash	80.7
Restricted Cash Other Than Proceeds from Successor Notes | Successor
Postconfirmation, Current Assets [Abstract]
Postconfirmation, restricted cash	26.0
Proceeds from Successor Notes | Effect of Plan
Fresh-Start Adjustment, Increase (Decrease), Assets [Abstract]
Fresh-start adjustment, increase (decrease), restricted cash	(1,000.0)
Proceeds from Successor Notes | Fresh Start Adjustments
Fresh-Start Adjustment, Increase (Decrease), Assets [Abstract]
Fresh-start adjustment, increase (decrease), restricted cash	0.0
Proceeds from Successor Notes | Predecessor
Preconfirmation, Current Assets [Abstract]
Preconfirmation, restricted cash	1,000.0
Proceeds from Successor Notes | Successor
Postconfirmation, Current Assets [Abstract]
Postconfirmation, restricted cash	$ 0.0