Supplemental Guarantor/Non-Guarantor Financial Information Textuals (Details)	9 Months Ended
Sep. 30, 2015
Percent of ownership of certain U.S. subsidiaries that fully and unconditionally guarantee the Senior Notes	100.00%

Percent of ownership of certain U.S. subsidiaries that fully and unconditionally guarantee the Senior Notes

No definition available.

Name:	btu_PercentofownershipofcertainU.S.subsidiariesthatfullyandunconditionallyguaranteetheSeniorNotes
Namespace Prefix:	btu_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration