XML 129 R116.htm IDEA: XBRL DOCUMENT
v3.7.0.1

Pension and Savings Plans (Details 5) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2016 | Dec. 31, 2015
Corporate Debt Securities [Member] |  |
Summary of changes in the fair value of the Master Trust's investments |  |
Fair value of plan assets at beginning of period | $ 259.4 |
Assets Held At Reporting Date: |  |
Fair value of plan assets at end of period | $ 265.7 | $ 259.4
Real Estate [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocations for assets of Master Trust | 2.00% | 3.00%
Equity Securities [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocations for assets of Master Trust |  | 31.00%
Fixed Income Investments [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocations for assets of Master Trust |  | 69.00%
Real Estate Investment [Member] |  |
Summary of changes in the fair value of the Master Trust's investments |  |
Fair value of plan assets at beginning of period | $ 23.0 |
Assets Held At Reporting Date: |  |
Fair value of plan assets at end of period | 14.1 | $ 23.0
Private Equity Funds [Member] |  |
Summary of changes in the fair value of the Master Trust's investments |  |
Fair value of plan assets at beginning of period | 183.9 |
Assets Held At Reporting Date: |  |
Fair value of plan assets at end of period | 186.1 | 183.9
Banks, Trust and Insurance, Equities [Member] |  |
Summary of changes in the fair value of the Master Trust's investments |  |
Fair value of plan assets at beginning of period | 97.3 |
Assets Held At Reporting Date: |  |
Fair value of plan assets at end of period | 109.0 | 97.3
Fair Value, Inputs, Level 2 [Member] |  |
Summary of changes in the fair value of the Master Trust's investments |  |
Fair value of plan assets at beginning of period | 301.0 |
Assets Held At Reporting Date: |  |
Fair value of plan assets at end of period | 301.0 | 301.0
Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member] |  |
Summary of changes in the fair value of the Master Trust's investments |  |
Fair value of plan assets at beginning of period | 259.4 |
Assets Held At Reporting Date: |  |
Fair value of plan assets at end of period | 265.7 | 259.4
Fair Value, Inputs, Level 2 [Member] | Real Estate Investment [Member] |  |
Summary of changes in the fair value of the Master Trust's investments |  |
Fair value of plan assets at beginning of period | 0.0 |
Assets Held At Reporting Date: |  |
Fair value of plan assets at end of period | 0.0 | 0.0
Level 3 [Member] |  |
Summary of changes in the fair value of the Master Trust's investments |  |
Fair value of plan assets at beginning of period | 23.0 |
Assets Held At Reporting Date: |  |
Fair value of plan assets at end of period | 14.1 | 23.0
Level 3 [Member] | Corporate Debt Securities [Member] |  |
Summary of changes in the fair value of the Master Trust's investments |  |
Fair value of plan assets at beginning of period | 0.0 |
Assets Held At Reporting Date: |  |
Fair value of plan assets at end of period | 0.0 | 0.0
Level 3 [Member] | Real Estate Investment [Member] |  |
Summary of changes in the fair value of the Master Trust's investments |  |
Fair value of plan assets at beginning of period | 23.0 | 30.2
Assets Held At Reporting Date: |  |
Realized gains | 1.8 | 3.2
Unrealized gains relatng to investments still held at the reporting date | 0.2 | 0.2
Purchases, sales and settlements, net | (10.9) | (10.6)
Fair value of plan assets at end of period | 14.1 | 23.0
Pension Plans, Defined Benefit [Member] |  |
Summary of changes in the fair value of the Master Trust's investments |  |
Fair value of plan assets at beginning of period | 757.3 | 839.8
Assets Held At Reporting Date: |  |
Fair value of plan assets at end of period | $ 773.0 | $ 757.3

X
- Definition Assets held at the reporting date. + References No definition available. + Details
Name: | btu_AssetsHeldAtReportingDateAbstract
Namespace Prefix: | btu_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Defined benefit plan actual return on plan assets unrealized during period. + References No definition available. + Details
Name: | btu_DefinedBenefitPlanActualReturnOnPlanAssetsUnrealizedDuringPeriod
Namespace Prefix: | btu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets still held. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(5)(iv)(02)(A) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsStillHeld
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
Name: | us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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

X
- Definition Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(5)(i) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from purchases, sales and settlements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(5)(iv)(02)(B) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanPurchasesSalesAndSettlements
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_RealEstateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_FixedIncomeInvestmentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_RealEstateInvestmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_PrivateEquityFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_BanksTrustAndInsuranceEquitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |