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Acquisition of Dearborn (Details2) (USD $)
Share data in Millions, except Per Share data, unless otherwise specified
0 Months Ended 12 Months Ended 3 Months Ended
Sep. 16, 2014
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2014
Business Acquisition [Line Items]          
Payments to Acquire Businesses, Net of Cash Acquired   $ 690,300,000us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired $ 0us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired $ 0us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired  
Stock Issued During Period, Shares, New Issues 40.25us-gaap_StockIssuedDuringPeriodSharesNewIssues        
Shares Issued, Price Per Share $ 9.00us-gaap_SharesIssuedPricePerShare        
Severstal Dearborn [Member]          
Business Acquisition [Line Items]          
Payments to Acquire Businesses, Net of Cash Acquired   690,300,000us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired
/ us-gaap_BusinessAcquisitionAxis
= aks_SeverstalDearbornMember
    13,100,000us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired
/ us-gaap_BusinessAcquisitionAxis
= aks_SeverstalDearbornMember
Business Combination, Additional Disclosures, Income Tax Charge   8,400,000aks_BusinessCombinationAdditionalDisclosuresIncomeTaxCharge
/ us-gaap_BusinessAcquisitionAxis
= aks_SeverstalDearbornMember
     
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate   4.49%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_BusinessAcquisitionAxis
= aks_SeverstalDearbornMember
     
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual   567,000,000us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual
/ us-gaap_BusinessAcquisitionAxis
= aks_SeverstalDearbornMember
     
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual   12,200,000us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual
/ us-gaap_BusinessAcquisitionAxis
= aks_SeverstalDearbornMember
     
Business Combination, Pro Forma, Asset Impairment Charge   1,005,100,000aks_BusinessCombinationProFormaAssetImpairmentCharge
/ us-gaap_BusinessAcquisitionAxis
= aks_SeverstalDearbornMember
43,000,000aks_BusinessCombinationProFormaAssetImpairmentCharge
/ us-gaap_BusinessAcquisitionAxis
= aks_SeverstalDearbornMember
   
Other Income (Expense) [Member] | Severstal Dearborn [Member]          
Business Acquisition [Line Items]          
Business Combination, Additional Disclosures, Unused Bridge Commitment Expensed   12,600,000aks_BusinessCombinationAdditionalDisclosuresUnusedBridgeCommitmentExpensed
/ us-gaap_BusinessAcquisitionAxis
= aks_SeverstalDearbornMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_OtherNonoperatingIncomeExpenseMember
     
Selling, General and Administrative Expenses [Member] | Severstal Dearborn [Member]          
Business Acquisition [Line Items]          
Business Combination, Acquisition Related Costs   8,100,000us-gaap_BusinessCombinationAcquisitionRelatedCosts
/ us-gaap_BusinessAcquisitionAxis
= aks_SeverstalDearbornMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SellingGeneralAndAdministrativeExpensesMember
     
Business Combination, Additional Disclosures, Severance Costs Expensed   2,600,000us-gaap_BusinessCombinationIntegrationRelatedCosts
/ us-gaap_BusinessAcquisitionAxis
= aks_SeverstalDearbornMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SellingGeneralAndAdministrativeExpensesMember
     
Senior Notes Due October 2021 [Member]          
Business Acquisition [Line Items]          
Debt Instrument, Face Amount   $ 430,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_LongtermDebtTypeAxis
= aks_SeniorNotesDueOctober2021Member
    $ 430,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_LongtermDebtTypeAxis
= aks_SeniorNotesDueOctober2021Member
Debt Instrument, Interest Rate, Stated Percentage (in hundredths)   7.625%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= aks_SeniorNotesDueOctober2021Member
    7.625%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= aks_SeniorNotesDueOctober2021Member
Debt Instrument, Maturity Date   Oct. 01, 2021      
Debt Instrument Offering Price   99.325%aks_DebtInstrumentOfferingPrice
/ us-gaap_LongtermDebtTypeAxis
= aks_SeniorNotesDueOctober2021Member
     
Weighted Average [Member] | Machinery and equipment [Member]          
Business Acquisition [Line Items]          
Property, Plant and Equipment, Useful Life   18 years      
Weighted Average [Member] | Machinery and equipment [Member] | Severstal Dearborn [Member]          
Business Acquisition [Line Items]          
Property, Plant and Equipment, Useful Life   20 years