Debt Capital Leases (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014
Debt Disclosure [Abstract]
Equity affiliate receivable and payable right of offset	$ 38.0

Equity Affiliate Receivable and Payable Right of Offset

No definition available.

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