Convertible Preferred Stock, Converted Shares, Equity Ownership Percent

No definition available.

Name:	btu_ConvertiblePreferredStockConvertedSharesEquityOwnershipPercent
Namespace Prefix:	btu_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Convertible Preferred Stock, Converted Shares, Fair Value

+ References

No definition available.

+ Details

Name:	btu_ConvertiblePreferredStockConvertedSharesFairValue
Namespace Prefix:	btu_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Credit-adjusted, risk-free interest rates.

+ References

No definition available.

+ Details

Name:	btu_CreditAdjustedRiskFreeInterestRates
Namespace Prefix:	btu_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Dividends, Common Stock, Paid In Kind, Annual Stated Rate

+ References

No definition available.

+ Details

Name:	btu_DividendsCommonStockPaidInKindAnnualStatedRate
Namespace Prefix:	btu_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Dividends, Common Stock, Paid In Kind, Guaranteed Period

+ References

No definition available.

+ Details

Name:	btu_DividendsCommonStockPaidInKindGuaranteedPeriod
Namespace Prefix:	btu_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Finite-Lived Intangible Assets, Fair Value Disclosure, Noncurrent

+ References

No definition available.

+ Details

Name:	btu_FiniteLivedIntangibleAssetsFairValueDisclosureNoncurrent
Namespace Prefix:	btu_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Incentive Plan Expiration Period

+ References

No definition available.

+ Details

Name:	btu_IncentivePlanExpirationPeriod
Namespace Prefix:	btu_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Liabilities, Held For Sale

+ References

No definition available.

+ Details

Name:	btu_LiabilitiesHeldForSale
Namespace Prefix:	btu_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Postconfirmation, Common Stock, Initial Share Price Estimate

+ References

No definition available.

+ Details

Name:	btu_PostconfirmationCommonStockInitialSharePriceEstimate
Namespace Prefix:	btu_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Postconfirmation, Common Stock, Share Price

+ References

No definition available.

+ Details

Name:	btu_PostconfirmationCommonStockSharePrice
Namespace Prefix:	btu_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Postconfirmation, Discounted Cash Flow, Estimated Weighed Average Cost Of Capital, Percent

+ References

No definition available.

+ Details

Name:	btu_PostconfirmationDiscountedCashFlowEstimatedWeighedAverageCostOfCapitalPercent
Namespace Prefix:	btu_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Postconfirmation, Stockholders' Equity Attributable to Parent

+ References

No definition available.

+ Details

Name:	btu_PostconfirmationStockholdersEquityAttributabletoParent
Namespace Prefix:	btu_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Preferred Stock, Conversion, Discount Percent Of Common Stock Value

+ References

No definition available.

+ Details

Name:	btu_PreferredStockConversionDiscountPercentOfCommonStockValue
Namespace Prefix:	btu_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Write Off Of Mine Development Costs

+ References

No definition available.

+ Details

Name:	btu_WriteOffOfMineDevelopmentCosts
Namespace Prefix:	btu_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Write Off Of Prepaid Assets

+ References

No definition available.

+ Details

Name:	btu_WriteOffOfPrepaidAssets
Namespace Prefix:	btu_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Fair value portion of assets classified as held for sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19190-110258

+ Details

Name:	us-gaap_AssetsHeldForSaleLongLivedFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Aggregate number of common shares reserved for future issuance.

+ References

+ Details

Name:	us-gaap_CommonStockCapitalSharesReservedForFutureIssuance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Face amount or stated value per share of common stock.

+ References

+ Details

Name:	us-gaap_CommonStockParOrStatedValuePerShare
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

+ References

+ Details

Name:	us-gaap_CommonStockSharesIssued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21463-112644

+ Details

Name:	us-gaap_CommonStockSharesOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of shares issued for each share of convertible preferred stock that is converted.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21475-112644

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(27))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(28))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21506-112644

+ Details

Name:	us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DeferredFinanceCostsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(1)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Fair value portion of assets, excluding financial assets, that lack physical substance, having a limited useful life.

+ References

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_FreshStartAdjustmentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of increase (decrease) in obligation for pension benefits. Includes, but is not limited to, defined benefit or defined contribution plans. Excludes other postretirement benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

+ Details

Name:	us-gaap_IncreaseDecreaseInPensionPlanObligations
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Total long-term debt at the balance sheet date after fresh-start adjustments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 852
-SubTopic 10
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=84165509&loc=d3e56426-112766

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 852
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6918054&loc=SL2890621-112765

+ Details

Name:	us-gaap_PostconfirmationLongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of preferred stock at the balance sheet date after fresh-start adjustments.

+ References

+ Details

Name:	us-gaap_PostconfirmationPreferredStock
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Total stockholders' equity at the balance sheet date after fresh-start adjustments.

+ References

+ Details

Name:	us-gaap_PostconfirmationStockholdersEquity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Value, before forfeitures, of stock or other type of equity granted of any equity-based compensation plan other than an employee stock ownership plan (ESOP).

+ References

No definition available.

+ Details

Name:	us-gaap_StockGrantedDuringPeriodValueSharebasedCompensationGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_FreshStartAdjustmentsTypeOfFreshStartAdjustmentAxis=btu_EffectofReorganizationPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=us-gaap_SuccessorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=btu_A2017IncentivePlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=us-gaap_PredecessorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DividendsAxis=btu_PaidInKindMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=btu_SuccessorCreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=btu_TermLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=btu_A6.000SeniorSecuredNotesDue2022Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SeniorNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=btu_A6.375SeniorSecuredNotesDue2025Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=btu_SeniorSecuredTermLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=btu_SuccessorNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_CoalSupplyAgreementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_ContractBasedIntangibleAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	btu_InterestRateTypeAxis=btu_U.S.ObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	btu_InterestRateTypeAxis=btu_AustralianOperationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Additional Information (Details) - USD ($) $ / shares in Units, shares in Millions	Apr. 01, 2017	Dec. 31, 2018	Dec. 31, 2017	Apr. 03, 2017	Mar. 31, 2017	Feb. 15, 2017
Effect of Plan
Fresh-Start Adjustment [Line Items]
Assets held-for-sale					$ 228,500,000
Write off of mine development costs	$ 89,500,000
Write off of prepaid assets	$ 15,000,000
Successor
Fresh-Start Adjustment [Line Items]
Common stock, shares outstanding (in shares)	70.9	110.4	105.2
Postconfirmation, preferred stock	$ 1,305,400,000
Postconfirmation, total stockholders' equity	3,131,900,000
Postconfirmation, long-term debt	1,853,700,000
Debt issuance cost		$ 68,900,000	$ 59,400,000
Successor \| Effect of Plan
Fresh-Start Adjustment [Line Items]
Final equity value	$ 3,081,000,000
Postconfirmation, common stock, share price (in dollars per share)	$ 22.03
Common Stock, shares issued (in shares)	70.9
Common Stock, par value per share (in dollars per share)	$ 0.01
Postconfirmation, preferred stock	$ 750,000,000
Discount percent of common stock value	35.00%
Postconfirmation, common stock, initial share price estimate	$ 25.00
Dividends, common stock, paid in kind, guaranteed period	3 years
Dividends, common stock, paid in kind, annual stated rate	8.50%
Convertible preferred stock, shares issued upon conversion	46.2
Equity ownership percent	42.00%
Postconfirmation, total stockholders' equity	$ 3,105,000,000
Convertible preferred stock, converted shares, fair value	$ 1,305,400,000
Discount rate	4.10%		4.15%
Remeasurement reduction in pension liabilities	$ 9,200,000
2017 Incentive Plan \| Effect of Plan
Fresh-Start Adjustment [Line Items]
Common stock reserved for future issuance	14.0
Incentive plan expiration period	10 years
2017 Incentive Plan \| Predecessor \| Effect of Plan
Fresh-Start Adjustment [Line Items]
Common stock reserved for future issuance	14.0
Minimum \| Effect of Plan
Fresh-Start Adjustment [Line Items]
Final equity value	$ 4,200,000,000
Discounted cash flow, estimated weighed average cost of capital, percent	11.00%
Maximum \| Effect of Plan
Fresh-Start Adjustment [Line Items]
Final equity value	$ 4,900,000,000
Discounted cash flow, estimated weighed average cost of capital, percent	14.50%
Restricted Stock \| 2017 Incentive Plan \| Effect of Plan
Fresh-Start Adjustment [Line Items]
Fair value of stock granted	$ 80,000,000
Paid In Kind \| Successor \| Effect of Plan
Fresh-Start Adjustment [Line Items]
Convertible preferred stock, shares issued upon conversion	13.1
Successor Credit Agreement \| Senior Secured Term Loan due 2025, net of original issue discount \| Effect of Plan
Fresh-Start Adjustment [Line Items]
Principal amount				$ 950,000,000
Successor Credit Agreement \| Senior Secured Term Loan due 2025, net of original issue discount \| Successor
Fresh-Start Adjustment [Line Items]
Principal amount		$ 400,000,000
6.000% Senior Secured Notes due March 2022 \| Senior Notes \| Effect of Plan
Fresh-Start Adjustment [Line Items]
Principal amount						$ 500,000,000.0
6.375% Senior Secured Notes due March 2025 \| Senior Notes \| Effect of Plan
Fresh-Start Adjustment [Line Items]
Principal amount						$ 500,000,000.0
Senior Secured Term Loan \| Senior Secured Term Loan due 2025, net of original issue discount \| Effect of Plan
Fresh-Start Adjustment [Line Items]
Postconfirmation, long-term debt	$ 950,000,000
Debt issuance cost	37,300,000
Successor Notes \| Senior Notes \| Effect of Plan
Fresh-Start Adjustment [Line Items]
Debt issuance cost	49,500,000
Principal amount	1,000,000,000.0
Coal supply agreements \| Successor \| Effect of Plan
Fresh-Start Adjustment [Line Items]
Finite-lived intangible assets, fair value	314,900,000
Finite-lived intangible assets, fair value, noncurrent	58,700,000
Port And Rail Take Or Pay Contracts \| Successor \| Effect of Plan
Fresh-Start Adjustment [Line Items]
Finite-lived intangible assets, fair value	32,600,000
Liabilities, held-for-sale					$ 15,700,000
Finite-lived intangible assets, fair value, noncurrent	$ 83,600,000
U.S. Obligations [Member] \| Successor
Fresh-Start Adjustment [Line Items]
Credit adjusted risk free interest rates			9.36%
Australian Operations \| Successor
Fresh-Start Adjustment [Line Items]
Credit adjusted risk free interest rates			4.36%