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Nature of Operations and Significant Accounting Policies (Nature of Operations) (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 26, 2014
Dec. 27, 2013
Dec. 28, 2012
Restructuring Cost and Reserve [Line Items]      
Number of weeks in fiscal reporting calendar P52W P52W P52W
Number of weeks in fiscal quarter P13W    
Cost method, maximum percentage 20.00%csx_CostMethodInvestmentMaximumPercentageForTreatment    
Cash equivalents, maximum maturity period 3 months    
Short-term investments, minimum maturity period 3 months    
Short-term investments, maximum maturity period 1 year    
Allowance for doubtful accounts $ 41us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent $ 33us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent  
Goodwill 63us-gaap_Goodwill 64us-gaap_Goodwill  
Workforce Reduction Plan [Member] | Employee Severance [Member]      
Restructuring Cost and Reserve [Line Items]      
Expected number of positions to be reduced 300us-gaap_RestructuringAndRelatedCostExpectedNumberOfPositionsEliminated
/ us-gaap_RestructuringCostAndReserveAxis
= us-gaap_EmployeeSeveranceMember
/ us-gaap_RestructuringPlanAxis
= csx_WorkforceReductionPlanMember		    
Restructuring charges incurred 39us-gaap_RestructuringAndRelatedCostIncurredCost
/ us-gaap_RestructuringCostAndReserveAxis
= us-gaap_EmployeeSeveranceMember
/ us-gaap_RestructuringPlanAxis
= csx_WorkforceReductionPlanMember		    
Total expected restructuring charges $ 45us-gaap_RestructuringAndRelatedCostExpectedCost1
/ us-gaap_RestructuringCostAndReserveAxis
= us-gaap_EmployeeSeveranceMember
/ us-gaap_RestructuringPlanAxis
= csx_WorkforceReductionPlanMember