Name:	aci_AccountReceivableNumberofFactorsRequiredtoDetermineCostofAdvanceBackstoppingaLetterofCreditIssuedUndertheSecuritizationFacility
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Data Type:	xbrli:integerItemType
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Account Receivable Securitization, Program Fees, percentage

No definition available.

Name:	aci_AccountReceivableSecuritizationProgramFees
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Data Type:	num:percentItemType
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Debtor-in-Possession Financing, Amount Arranged, Number of Withdrawals Allowed

No definition available.

Name:	aci_DebtorinPossessionFinancingAmountArrangedNumberofWithdrawalsAllowed
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Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

Debtor-in-Possession Financing, Amount Arranged, Period of Availability

No definition available.

Name:	aci_DebtorinPossessionFinancingAmountArrangedPeriodofAvailability
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Debtor-in-Possession Financing, Carve-out for Claims

No definition available.

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

Debtor-in-Possession Financing, Customary Prepayments, Proceeds from Any Casualty Event

No definition available.

Name:	aci_DebtorinPossessionFinancingCustomaryPrepaymentsProceedsfromAnyCasualtyEvent
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Debtor-in-Possession Financing, Customary Prepayments, Proceeds from Sale or Disposition of Non-Ordinary Course Asset

No definition available.

Name:	aci_DebtorinPossessionFinancingCustomaryPrepaymentsProceedsfromSaleorDispositionofNonOrdinaryCourseAsset
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Data Type:	xbrli:monetaryItemType
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Debtor-in-Possession Financing, Customary Prepayments, Proceeds from Sale or Disposition of Non-Ordinary Course Asset, Individual Sale, Maximum

No definition available.

Name:	aci_DebtorinPossessionFinancingCustomaryPrepaymentsProceedsfromSaleorDispositionofNonOrdinaryCourseAssetIndividualSaleMaximum
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Data Type:	xbrli:monetaryItemType
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Debtor-in-Possession Financing, Financial Maintenance Covenant, Following the Entry of Final Order

No definition available.

Name:	aci_DebtorinPossessionFinancingFinancialMaintenanceCovenantFollowingtheEntryofFinalOrder
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Data Type:	xbrli:monetaryItemType
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Debtor-in-Possession Financing, Financial Maintenance Covenant, Prior to Entry of Final Order

No definition available.

Name:	aci_DebtorinPossessionFinancingFinancialMaintenanceCovenantPriortoEntryofFinalOrder
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Data Type:	xbrli:monetaryItemType
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The amount owed to the reporting entity by counterparties in securitized loan transactions.

No definition available.

Name:	us-gaap_AccountsReceivableFromSecuritization
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
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Data Type:	num:percentItemType
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Contractual interest rate for funds borrowed, under the debt agreement.

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

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
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Period Type:	instant

Amount debtor-in-possession financing arranged (but not necessarily all borrowed).

No definition available.

Name:	us-gaap_DebtorInPossessionFinancingAmountArranged
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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.

No definition available.

Name:	us-gaap_LineOfCreditFacilityLineItems
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Data Type:	xbrli:stringItemType
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Period Type:	duration

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
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Balance Type:
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Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateFloorMember
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Data Type:	na
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Period Type:

Name:	us-gaap_VariableRateAxis=us-gaap_BaseRateMember
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Data Type:	na
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Name:	us-gaap_LongtermDebtTypeAxis=aci_SevenPointZeroZeroSeniorNotesDueJuneFifteenTwoThousandNineteenMember
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Data Type:	na
Balance Type:
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Name:	us-gaap_LongtermDebtTypeAxis=aci_A9875SeniorNotesDue2019Member
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Period Type:

Name:	us-gaap_LongtermDebtTypeAxis=aci_A8.00SeniorSecuredNotesdue2019Member
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Name:	us-gaap_LongtermDebtTypeAxis=aci_SevenPointTwoFiveSeniorNotesDueOctoberOneTwoThousandTwentyMember
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