Credit Exposure Related to Coal Trading Activities

No definition available.

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

- Definition

Potential collateralization that may be requested by counterparties due to a material adverse event.

+ References

No definition available.

+ Details

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

- Definition

Amount of right to receive cash collateral under master netting arrangements that have not been offset against derivative liabilities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226016-175313

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=d3e41678-113959

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (d)(2)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

+ Details

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

- Definition

Cap rate on a foreign currency derivative for example, but not limited to, a cap or a collar.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeExchangeRateCap1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

The net amount as of the balance sheet date of the fair value of derivative assets and derivative liabilities that in accordance with the entity's accounting policy were offset against collateral under a master netting arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=d3e41678-113959

+ Details

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

- Definition

Nominal number of units used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5579245-113959

+ Details

Name:	us-gaap_DerivativeNonmonetaryNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

+ Details

Name:	us-gaap_DerivativeNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
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_DerivativesFairValueLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value as of the balance sheet date of interest rate derivative assets, net of interest rate derivative liabilities, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized on the balance sheet.

+ References

No definition available.

+ Details

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

- Definition

Amount receivable from broker-dealers and clearing organizations, including, but not limited to, securities failed-to-deliver, certain deposits for securities borrowed, open transactions, good faith and margin deposits, commissions and floor brokerage receivables.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=118952595&loc=d3e4428-111522

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 20
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=35710130&loc=d3e41645-110958

+ Details

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

- Details

Name:	us-gaap_TradingActivityByTypeAxis=btu_CoalTradingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ExternalCreditRatingByGroupingAxis=us-gaap_ExternalCreditRatingInvestmentGradeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=btu_CoalTradingPositionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByTypeAxis=us-gaap_CreditConcentrationRiskMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ExternalCreditRatingByGroupingAxis=btu_NonRatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForeignExchangeContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_PublicUtilitiesInventoryCoalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=btu_DieselFuelHedgeContractsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementScenarioAxis=srt_ScenarioForecastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Derivatives and Fair Value Measurements Texuals (Details) T in Millions, $ in Millions, $ in Millions	Dec. 31, 2020 T	Sep. 30, 2020 $ / $	Dec. 31, 2019 USD ($) T	Dec. 31, 2019 AUD ($) T	Dec. 31, 2018 USD ($)
Coal Trading
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net			$ 22.1		$ 21.8
Derivative, Collateral, Right to Reclaim Cash			7.9		16.7
Receivables from Brokers-Dealers and Clearing Organizations			1.3		2.2
Potential collateralization that may be requested by counterparties due to a material adverse event			$ 0.0		$ 1.3
External Credit Rating, Investment Grade \| Coal Trading Positions \| Credit Concentration Risk \| Coal Trading
Derivatives, Fair Value [Line Items]
Credit Exposure Related to Coal Trading Activities			91.00%	91.00%
Non Rated \| Coal Trading Positions \| Credit Concentration Risk \| Coal Trading
Derivatives, Fair Value [Line Items]
Credit Exposure Related to Coal Trading Activities			9.00%	9.00%
Foreign currency option contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount				$ 925.0
Foreign currency option contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount				$ 0.0
Coal
Derivatives, Fair Value [Line Items]
Derivative, Nonmonetary Notional Amount \| T			2.0	2.0
Diesel Fuel Hedge Contracts
Derivatives, Fair Value [Line Items]
Interest Rate Derivatives, at Fair Value, Net				$ 0.0
Scenario, Forecast \| Foreign currency option contracts \| Minimum
Derivatives, Fair Value [Line Items]
Derivative, Exchange Rate Cap \| $ / $		0.73
Scenario, Forecast \| Foreign currency option contracts \| Maximum
Derivatives, Fair Value [Line Items]
Derivative, Exchange Rate Cap \| $ / $		0.75
Scenario, Forecast \| Coal
Derivatives, Fair Value [Line Items]
Derivative, Nonmonetary Notional Amount \| T	1.7