1.0.0.3 false Condensed Consolidated Balance Sheets (USD $) In Millions false 1 $ false false Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 Unit1 Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 2 $ false false Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 Unit1 Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 8 Current assets 6 us-gaap_CashAndCashEquivalentsAtCarryingValueAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. false 9 Cash and cash equivalents 7 us-gaap_CashAndCashEquivalentsAtCarryingValue us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 true true 790800000 790.8 false false 2 true true 449700000 449.7 false false No definition available. No authoritative reference available. false 10 Accounts receivable, net of allowance for doubtful accounts of $17.7 at September 30, 2009 and $24.8 at December 31, 2008 7 us-gaap_AccountsReceivableNetCurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 339800000 339.8 false false 2 false true 382200000 382.2 false false No definition available. No authoritative reference available. false 11 Inventories 7 us-gaap_InventoryNet us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 357200000 357.2 false false 2 false true 276200000 276.2 false false No definition available. No authoritative reference available. false 12 Assets from coal trading activities, net 7 btu_AssetsFromCoalTradingActivitiesNet btu false debit instant monetary Assets From Coal Trading Activities, Net false false false false false false false false false 1 false true 360400000 360.4 false false 2 false true 662800000 662.8 false false Assets From Coal Trading Activities, Net No authoritative reference available. false 13 Deferred income taxes 7 us-gaap_DeferredTaxAssetsNetCurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 12500000 12.5 false false 2 false true 1700000 1.7 false false No definition available. No authoritative reference available. false 14 Other current assets 7 us-gaap_OtherAssetsCurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 228400000 228.4 false false 2 false true 198700000 198.7 false false No definition available. No authoritative reference available. true 15 Total current assets 7 us-gaap_AssetsCurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 2089100000 2089.1 false false 2 false true 1971300000 1971.3 false false No definition available. No authoritative reference available. false 18 Property, plant, equipment and mine development 6 us-gaap_PropertyPlantAndEquipmentGrossAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. false 19 Land and coal interests 7 us-gaap_Land us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 7505400000 7505.4 false false 2 false true 7349400000 7349.4 false false No definition available. No authoritative reference available. false 20 Buildings and improvements 7 us-gaap_BuildingsAndImprovementsGross us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 887700000 887.7 false false 2 false true 858100000 858.1 false false No definition available. No authoritative reference available. false 21 Machinery and equipment 7 us-gaap_MachineryAndEquipmentGross us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 1315100000 1315.1 false false 2 false true 1245100000 1245.1 false false No definition available. No authoritative reference available. false 22 Less: accumulated depreciation, depletion and amortization 6 us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true -2480000000 -2480.0 false false 2 false true -2155300000 -2155.3 false false No definition available. No authoritative reference available. true 23 Property, plant, equipment and mine development, net 6 us-gaap_PropertyPlantAndEquipmentNet us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 7228200000 7228.2 false false 2 false true 7297300000 7297.3 false false No definition available. No authoritative reference available. false 24 Investments and other assets 6 us-gaap_OtherAssetsNoncurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 542200000 542.2 false false 2 false true 427000000 427.0 false false No definition available. No authoritative reference available. true 25 Total assets 6 us-gaap_Assets us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 9859500000 9859.5 false false 2 false true 9695600000 9695.6 false false No definition available. No authoritative reference available. true 28 Current liabilities 5 us-gaap_LiabilitiesCurrentAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. false 29 Current maturities of long-term debt 6 us-gaap_LongTermDebtCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 13700000 13.7 false false 2 false true 17000000 17.0 false false No definition available. No authoritative reference available. false 30 Liabilities from coal trading activities, net 6 btu_LiabilitiesFromCoalTradingActivitiesNet btu false credit instant monetary Liabilities from coal trading activities, net false false false false false false false false false 1 false true 121300000 121.3 false false 2 false true 304200000 304.2 false false Liabilities from coal trading activities, net No authoritative reference available. false 31 Accounts payable and accrued expenses 6 us-gaap_AccountsPayableCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 1188400000 1188.4 false false 2 false true 1535000000 1535.0 false false No definition available. No authoritative reference available. true 32 Total current liabilities 6 us-gaap_LiabilitiesCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 1323400000 1323.4 false false 2 false true 1856200000 1856.2 false false No definition available. No authoritative reference available. false 33 Long-term debt, less current maturities 6 us-gaap_LongTermDebtAndCapitalLeaseObligations us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 2763200000 2763.2 false false 2 false true 2776600000 2776.6 false false No definition available. No authoritative reference available. false 34 Deferred income taxes 6 us-gaap_DeferredTaxLiabilitiesNoncurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 344900000 344.9 false false 2 false true 20800000 20.8 false false No definition available. No authoritative reference available. false 35 Asset retirement obligations 6 us-gaap_MineReclamationAndClosingLiabilityNoncurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 431200000 431.2 false false 2 false true 418700000 418.7 false false No definition available. No authoritative reference available. false 36 Accrued postretirement benefit costs 6 us-gaap_OtherPostretirementDefinedBenefitPlanLiabilitiesNoncurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 767300000 767.3 false false 2 false true 766000000 766.0 false false No definition available. No authoritative reference available. false 37 Other noncurrent liabilities 6 us-gaap_OtherLiabilitiesNoncurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 444800000 444.8 false false 2 false true 737800000 737.8 false false No definition available. No authoritative reference available. true 38 Total liabilities 6 us-gaap_Liabilities us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 6074800000 6074.8 false false 2 false true 6576100000 6576.1 false false No definition available. No authoritative reference available. false 40 Stockholders' equity 5 us-gaap_StockholdersEquityAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. false 41 Preferred Stock - $0.01 per share par value; 10,000,000 shares authorized, no shares issued or outstanding as of September 30, 2009 or December 31, 2008 6 us-gaap_PreferredStockValue us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 0 0 false false 2 false true 0 0 false false No definition available. No authoritative reference available. false 42 Series A Junior Participating Preferred Stock - 1,500,000 shares authorized, no shares issued or outstanding as of September 30, 2009 or December 31, 2008 6 btu_SeriesJuniorParticipatingPreferredStock1500000SharesAuthorizedNoSharesIssuedOrOutstandingAsOfSeptember302009OrDecember312008 btu false credit instant monetary Each outstanding share of common stock, par value $0.01 per share, of the Company carries one preferred share purchase right... false false false false false false false false false 1 false true 0 0 false false 2 false true 0 0 false false Each outstanding share of common stock, par value $0.01 per share, of the Company carries one preferred share purchase right (a Right). The Rights are governed by a plan that expires in August 2012. No authoritative reference available. false 43 Perpetual Preferred Stock - 750,000 shares authorized, no shares issued or outstanding as of September 30, 2009 or December 31, 2008 6 btu_PerpetualPreferredStock750000SharesAuthorizedNoSharesIssuedOrOutstandingAsOfSeptember302009OrDecember312009 btu false credit instant monetary The perpetual preferred stock has a liquidation preference of $1,000 per share, is not convertible and is redeemable at the... false false false false false false false false false 1 false true 0 0 false false 2 false true 0 0 false false The perpetual preferred stock has a liquidation preference of $1,000 per share, is not convertible and is redeemable at the Company's option at any time at a cash redemption price per share equal to the liquidation preference plus any accumulated dividends. No authoritative reference available. false 44 Series Common Stock - $0.01 per share par value; 40,000,000 shares authorized, no shares issued or outstanding as of September 30, 2009 or December 31, 2008 6 btu_SeriesCommonStock001PerShareParValue40000000SharesAuthorizedNoSharesIssuedOrOutstandingAsOfSeptember302009OrDecember312008 btu false credit instant monetary The BOD is authorized to determine the terms and rights of the series, including the number of authorized shares, whether... false false false false false false false false false 1 false true 0 0 false false 2 false true 0 0 false false The BOD is authorized to determine the terms and rights of the series, including the number of authorized shares, whether dividends (if any) will be cumulative or non-cumulative and the dividend rate of the series, redemption or sinking fund provisions, conversion terms, prices and rates, and amounts payable on shares of the series in the event of any voluntary or involuntary liquidation, dissolution or winding up of the affairs of the Company. The BOD may also determine restrictions on the issuance of shares of the same series or of any other class or series, and the voting rights (if any) of the holders of the series. No authoritative reference available. false 45 Common Stock - $0.01 per share par value; 800,000,000 shares authorized, 276,370,726 shares issued and 267,728,748 shares outstanding as of September 30, 2009 and 275,211,240 shares issued and 266,644,979 shares outstanding as of December 31, 2008 6 us-gaap_CommonStockValue us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 2800000 2.8 false false 2 false true 2800000 2.8 false false No definition available. No authoritative reference available. false 46 Additional paid-in capital 6 us-gaap_AdditionalPaidInCapital us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 2054400000 2054.4 false false 2 false true 2020200000 2020.2 false false No definition available. No authoritative reference available. false 47 Retained earnings 6 us-gaap_RetainedEarningsAccumulatedDeficit us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 2110300000 2110.3 false false 2 false true 1802400000 1802.4 false false No definition available. No authoritative reference available. false 48 Accumulated other comprehensive loss 6 us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true -65900000 -65.9 false false 2 false true -388500000 -388.5 false false No definition available. No authoritative reference available. false 49 Treasury shares, at cost: 8,641,978 shares as of September 30, 2009 and 8,566,261 shares as of December 31, 2008 6 us-gaap_TreasuryStockValue us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true -321000000 -321.0 false false 2 false true -318800000 -318.8 false false No definition available. No authoritative reference available. true 50 Peabody Energy Corporation's stockholders' equity 6 us-gaap_StockholdersEquity us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 3780600000 3780.6 false false 2 false true 3118100000 3118.1 false false No definition available. No authoritative reference available. false 51 Noncontrolling interests 6 us-gaap_MinorityInterest us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 4100000 4.1 false false 2 false true 1400000 1.4 false false No definition available. No authoritative reference available. true 52 Total stockholders' equity 6 us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 3784700000 3784.7 false false 2 false true 3119500000 3119.5 false false No definition available. No authoritative reference available. true 53 Total liabilities and stockholders' equity 6 us-gaap_LiabilitiesAndStockholdersEquity us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 true true 9859500000 9859.5 false false 2 true true 9695600000 9695.6 false false No definition available. No authoritative reference available. true false 2 41 false HundredThousands UnKnown UnKnown false true