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Property, Plant, Equipment and Mine Development - Narrative (Details)	Mar. 31, 2021 USD ($)
Impaired Long-Lived Assets Held and Used [Line Items]
At-risk assets	$ 1,200,000,000
Other US Mining Operations
Impaired Long-Lived Assets Held and Used [Line Items]
At-risk assets	$ 0

X

- Definition

At-risk assets

+ References

No definition available.

+ Details

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

X

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

X

- Details

Name:	btu_MineLocationAxis=btu_OtherUSMiningOperationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: