Percentage price of original principal amount of debt at which debt was issued.

No definition available.

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Namespace Prefix:	btu_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Aggregate principal amount of the 2016 Senior notes that were redeemed by the Company.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Percentage amount of the aggregate principal amount of the Second Lien Notes the Company may redeem prior to March 15, 2018.

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
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Period Type:	duration

- Definition

Redemption price of bonds as percentage of principal amount plus a make-whole premium and any accrued unpaid interest to the redemption date.

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
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- Definition

Amount represents the tender offer premiums paid on the 2016 Senior Notes repurchase.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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=34725769&loc=d3e28878-108400

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-Topic 835
-SubTopic 30
-Section 45
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-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ 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 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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- 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

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Balance Type:	na
Period Type:	duration

- Definition

Fair value amount of debt instrument that was repurchased.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Face (par) amount of the original debt instrument that was repurchased.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of debt discount that was originally recognized at the issuance of the instrument that has yet to be amortized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
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-Paragraph 1A
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Balance Type:	debit
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- Definition

Amount of debt issuance costs (for example, but not limited to, legal, accounting, broker, and regulatory fees).

+ References

No definition available.

+ Details

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Balance Type:	debit
Period Type:	duration

- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 50
-Section 40
-Paragraph 2
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Balance Type:	credit
Period Type:	duration

- Definition

Write-off of amounts previously capitalized as debt issuance cost in an extinguishment of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.8)
-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

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Debt Senior Secured Second Lien Notes (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Redemption price of senior notes as percentage of principal amount plus a make whole premium and any accrued unpaid interest to the redemption date			100.00%
Loss on early debt extinguishment	$ (8.3)	$ (59.5)	$ (67.8)	$ (1.6)	$ (16.9)
10.00% Senior Secured Second Lien Notes Due 2022 [Member]
Debt Instrument [Line Items]
Face amount of senior notes			$ 1,000.0
Stated interest rate - percentage			10.00%
Redemption price of senior notes as percentage of principal amount plus a make whole premium and any accrued unpaid interest to the redemption date			100.00%
Redeemable Percent of the Aggregate Principal Amount of the Second Lien Notes			35.00%
Debt Instrument Issue Price Percentage			97.566%
Debt instrument, unamortized discount			$ 24.3
Debt Issuance Cost			$ 16.9
7.375% Senior Notes due November 2016 [Member]
Debt Instrument [Line Items]
Stated interest rate - percentage			7.375%
Debt Instrument, Repurchased Face Amount			$ 650.0
Debt Instrument, Repurchase Amount			566.9
Debt Instrument Redemption 2016 Notes			83.1
Loss on early debt extinguishment			(67.8)
Tender Offer Premiums Paid on 2016 Senior Notes Repurchase			66.4
Write-off of debt issuance costs			$ 1.4