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Income Taxes - Loss Carryforwards (Details 4) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Tax Credit Carryforward [Line Items]    
Deferred tax assets from operating loss and tax credit carryforwards 778.1aks_DeferredTaxAssetsOperatingLossAndTaxCreditCarryforwards $ 663.5aks_DeferredTaxAssetsOperatingLossAndTaxCreditCarryforwards
Domestic Tax Authority [Member] | Operating Loss Carryforward [Member]    
Tax Credit Carryforward [Line Items]    
Operating Loss Carryforwards 2,154.4us-gaap_OperatingLossCarryforwards
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_DomesticCountryMember
/ us-gaap_TaxCreditCarryforwardAxis
= aks_OperatingLossCarryforwardMember		  
Domestic Tax Authority [Member] | Alternative Minimum Tax [Member]    
Tax Credit Carryforward [Line Items]    
Operating Loss Carryforwards 2,336.2us-gaap_OperatingLossCarryforwards
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_DomesticCountryMember
/ us-gaap_TaxCreditCarryforwardAxis
= aks_AlternativeMinimumTaxMember		  
Tax Credit Carryforward, Amount 18.9us-gaap_TaxCreditCarryforwardAmount
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_DomesticCountryMember
/ us-gaap_TaxCreditCarryforwardAxis
= aks_AlternativeMinimumTaxMember		  
Domestic Tax Authority [Member] | Research [Member]    
Tax Credit Carryforward [Line Items]    
Tax Credit Carryforward, Amount 1.2us-gaap_TaxCreditCarryforwardAmount
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_DomesticCountryMember
/ us-gaap_TaxCreditCarryforwardAxis
= us-gaap_ResearchMember		  
State and Local Jurisdiction [Member] | Operating Loss and Tax Credit Carryforwards [Member]    
Tax Credit Carryforward [Line Items]    
Deferred tax assets from operating loss and tax credit carryforwards 82.3aks_DeferredTaxAssetsOperatingLossAndTaxCreditCarryforwards
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_StateAndLocalJurisdictionMember
/ us-gaap_TaxCreditCarryforwardAxis
= aks_OperatingLossandTaxCreditCarryforwardsMember		  
Earliest Tax Year [Member] | Domestic Tax Authority [Member]    
Tax Credit Carryforward [Line Items]    
Operating Loss Carryforwards, Expiration Dates Dec. 31, 2023  
Earliest Tax Year [Member] | Domestic Tax Authority [Member] | Research [Member]    
Tax Credit Carryforward [Line Items]    
Tax Credit Carryforward, Expiration Date Dec. 31, 2027  
Earliest Tax Year [Member] | State and Local Jurisdiction [Member] | Operating Loss and Tax Credit Carryforwards [Member]    
Tax Credit Carryforward [Line Items]    
Operating Loss and Tax Credit Carryforwards, Expiration Date Dec. 31, 2015  
Latest Tax Year [Member] | Domestic Tax Authority [Member]    
Tax Credit Carryforward [Line Items]    
Operating Loss Carryforwards, Expiration Dates Dec. 31, 2034  
Latest Tax Year [Member] | State and Local Jurisdiction [Member] | Operating Loss and Tax Credit Carryforwards [Member]    
Tax Credit Carryforward [Line Items]    
Operating Loss and Tax Credit Carryforwards, Expiration Date Dec. 31, 2034