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Related Party Transactions (Narrative) (Details) (Corporate Joint Venture [Member], USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 26, 2014
Dec. 27, 2013
Dec. 28, 2012
Related Party Transaction [Line Items]      
Difference between carrying amount and underlying equity $ 355us-gaap_EquityMethodInvestmentDifferenceBetweenCarryingAmountAndUnderlyingEquity    
Interest expense 3us-gaap_InterestExpenseRelatedParty 4us-gaap_InterestExpenseRelatedParty 4us-gaap_InterestExpenseRelatedParty
Economic interest in related party which is also an equity method investment [Member]      
Related Party Transaction [Line Items]      
Percentage economic interest in related party 42.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ csx_EconomicinterestAxis
= csx_EconomicinterestinrelatedpartywhichisalsoanequitymethodinvestmentMember
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= us-gaap_CorporateJointVentureMember
   
Voting interest in related party which is also an equity method investment [Member]      
Related Party Transaction [Line Items]      
Percentage economic interest in related party 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= us-gaap_CorporateJointVentureMember
/ csx_VotinginterestAxis
= csx_VotinginterestinrelatedpartywhichisalsoanequitymethodinvestmentMember
   
Long-term Debt [Member] | CSXT Promissory Note Related Party October 2044 [Member]      
Related Party Transaction [Line Items]      
Promissory Notes Payable to Conrail Subsidiary 151us-gaap_NotesPayableRelatedPartiesNoncurrent
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_LongTermDebtMember
/ us-gaap_DebtInstrumentAxis
= csx_CSXTPromissoryNoteRelatedPartyOctober2044Member
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= us-gaap_CorporateJointVentureMember
[1]    
Notes issued, interest rate 2.89%us-gaap_RelatedPartyTransactionRate
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_LongTermDebtMember
/ us-gaap_DebtInstrumentAxis
= csx_CSXTPromissoryNoteRelatedPartyOctober2044Member
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= us-gaap_CorporateJointVentureMember
[1]    
Long-term Debt [Member] | CSXT Promissory Note Related Party March 2035 [Member]      
Related Party Transaction [Line Items]      
Promissory Notes Payable to Conrail Subsidiary   23us-gaap_NotesPayableRelatedPartiesNoncurrent
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_LongTermDebtMember
/ us-gaap_DebtInstrumentAxis
= csx_CSXTPromissoryNoteRelatedPartyMarch2035Member
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= us-gaap_CorporateJointVentureMember
 
Notes issued, interest rate 4.52%us-gaap_RelatedPartyTransactionRate
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_LongTermDebtMember
/ us-gaap_DebtInstrumentAxis
= csx_CSXTPromissoryNoteRelatedPartyMarch2035Member
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= us-gaap_CorporateJointVentureMember
4.52%us-gaap_RelatedPartyTransactionRate
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_LongTermDebtMember
/ us-gaap_DebtInstrumentAxis
= csx_CSXTPromissoryNoteRelatedPartyMarch2035Member
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= us-gaap_CorporateJointVentureMember
 
Long-term Debt [Member] | CSX Promissory Note Related Party October 2035 [Member]      
Related Party Transaction [Line Items]      
Promissory Notes Payable to Conrail Subsidiary   $ 73us-gaap_NotesPayableRelatedPartiesNoncurrent
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_LongTermDebtMember
/ us-gaap_DebtInstrumentAxis
= csx_CSXPromissoryNoteRelatedPartyOctober2035Member
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= us-gaap_CorporateJointVentureMember
 
Notes issued, interest rate 4.40%us-gaap_RelatedPartyTransactionRate
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_LongTermDebtMember
/ us-gaap_DebtInstrumentAxis
= csx_CSXPromissoryNoteRelatedPartyOctober2035Member
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= us-gaap_CorporateJointVentureMember
4.40%us-gaap_RelatedPartyTransactionRate
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_LongTermDebtMember
/ us-gaap_DebtInstrumentAxis
= csx_CSXPromissoryNoteRelatedPartyOctober2035Member
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= us-gaap_CorporateJointVentureMember
 
[1] Promissory notes payable to Conrail are included on the consolidated balance sheet of CSX as long-term debt.