XML 32 R104.htm IDEA: XBRL DOCUMENT v2.4.1.9
Postretirement Health Care and Life Insurance Benefits (Details 3) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Postretirement Health Care and Life Insurance Benefits [Member]      
Weighted-average assumptions used to determine benefit obligations      
Discount rate 4.10%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
4.90%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Measurement date Dec. 31, 2014 Dec. 31, 2013  
Weighted-average assumptions used to determine net periodic benefit cost      
Discount rate 4.90%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
4.21%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
5.05%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Measurement date December 31, 2013 December 31, 2012 December 31, 2011
Assumed health care cost trend rates, One percentage point increase      
One Percentage-Point Increase Effect on total service and interest cost components $ 4.1us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointIncreaseOnServiceAndInterestCostComponents
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
[1]    
One Percentage-Point Decrease Effect on total service and interest cost component (3.8)us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointDecreaseOnServiceAndInterestCostComponents1
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
[1]    
One Percentage-Point Increase Effect on total postretirement benefit obligation 80.6us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointIncreaseOnAccumulatedPostretirementBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
[1]    
One Percentage-Point Decrease Effect on total postretirement benefit obligation $ (70.3)us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointDecreaseOnAccumulatedPostretirementBenefitObligation1
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
[1]    
Pre-Medicare [Member]      
Assumed health care cost trend rate      
Health care cost trend rate assumed for next year 7.00%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= btu_PreMedicareMember
6.26%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= btu_PreMedicareMember
 
Rate to which the cost trend is assumed to decline (the ultimate trend rate) 4.75%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= btu_PreMedicareMember
4.67%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= btu_PreMedicareMember
 
Year that the rate reaches the ultimate trend rate 2021 2023  
Post-Medicare [Member]      
Assumed health care cost trend rate      
Health care cost trend rate assumed for next year 6.00%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= btu_PostMedicareMember
6.26%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= btu_PostMedicareMember
 
Rate to which the cost trend is assumed to decline (the ultimate trend rate) 4.75%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= btu_PostMedicareMember
4.67%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= btu_PostMedicareMember
 
Year that the rate reaches the ultimate trend rate 2021 2023  
[1] In addition to the effect on total service and interest cost components of expense, changes in trend rates would also increase or decrease the actuarial gain or loss amortization expense component. The impact on actuarial gain or loss amortization would approximate the increase or decrease in the obligation divided by 11.70 years at January 1, 2015.