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Nature of Operations and Significant Accounting Policies (Business) (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 12 Months Ended
Dec. 26, 2014
states
mi
railroads
employees
Sep. 26, 2014
Jun. 27, 2014
Mar. 28, 2014
Dec. 27, 2013
Sep. 27, 2013
Jun. 28, 2013
Mar. 29, 2013
Dec. 26, 2014
employees
states
mi
railroads
Dec. 27, 2013
Dec. 28, 2012
Revenue from External Customer [Line Items]                      
Entity Number of Employees 32,000dei_EntityNumberOfEmployees               32,000dei_EntityNumberOfEmployees    
Number of Union Employees                 26,000csx_NumberOfUnionEmployees    
Total number of rail route miles 21,000csx_RailRouteNetworkDistance               21,000csx_RailRouteNetworkDistance    
Rail network states number 23us-gaap_NumberOfStatesInWhichEntityOperates               23us-gaap_NumberOfStatesInWhichEntityOperates    
Number of short-line and regional railroads served 240csx_NumberOfShortLineAndRegionalRailroadsServed               240csx_NumberOfShortLineAndRegionalRailroadsServed    
Revenue $ 3,192us-gaap_SalesRevenueNet $ 3,221us-gaap_SalesRevenueNet $ 3,244us-gaap_SalesRevenueNet $ 3,012us-gaap_SalesRevenueNet $ 3,032us-gaap_SalesRevenueNet $ 2,985us-gaap_SalesRevenueNet $ 3,046us-gaap_SalesRevenueNet $ 2,963us-gaap_SalesRevenueNet $ 12,669us-gaap_SalesRevenueNet $ 12,026us-gaap_SalesRevenueNet $ 11,763us-gaap_SalesRevenueNet
Minimum [Member]                      
Revenue from External Customer [Line Items]                      
Number of ocean, river and lake ports serviced (more than 70) 70csx_NumberOfOceanRiverAndLakePortsServiced
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		               70csx_NumberOfOceanRiverAndLakePortsServiced
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		    
Merchandise business [Member]                      
Revenue from External Customer [Line Items]                      
Number of carloads                 2,900,000csx_NumberOfCarloads
/ us-gaap_ProductOrServiceAxis
= csx_MerchandiseBusinessMember		    
Percentage of total revenue                 60.00%csx_PercentageOfTotalRevenue
/ us-gaap_ProductOrServiceAxis
= csx_MerchandiseBusinessMember		    
Percentage of total volume                 42.00%csx_PercentageOfTotalVolume
/ us-gaap_ProductOrServiceAxis
= csx_MerchandiseBusinessMember		    
Coal business [Member]                      
Revenue from External Customer [Line Items]                      
Number of carloads                 1,300,000csx_NumberOfCarloads
/ us-gaap_ProductOrServiceAxis
= csx_CoalBusinessMember		    
Percentage of total revenue                 22.00%csx_PercentageOfTotalRevenue
/ us-gaap_ProductOrServiceAxis
= csx_CoalBusinessMember		    
Percentage of total volume                 18.00%csx_PercentageOfTotalVolume
/ us-gaap_ProductOrServiceAxis
= csx_CoalBusinessMember		    
Intermodal business [Member]                      
Revenue from External Customer [Line Items]                      
Percentage of total revenue                 14.00%csx_PercentageOfTotalRevenue
/ us-gaap_ProductOrServiceAxis
= csx_IntermodalBusinessMember		    
Percentage of total volume                 40.00%csx_PercentageOfTotalVolume
/ us-gaap_ProductOrServiceAxis
= csx_IntermodalBusinessMember		    
Number of terminals (more than 50) 50csx_MinimumNumberOfTerminals
/ us-gaap_ProductOrServiceAxis
= csx_IntermodalBusinessMember		               50csx_MinimumNumberOfTerminals
/ us-gaap_ProductOrServiceAxis
= csx_IntermodalBusinessMember		    
Other business [Member]                      
Revenue from External Customer [Line Items]                      
Percentage of total revenue                 4.00%csx_PercentageOfTotalRevenue
/ us-gaap_ProductOrServiceAxis
= csx_OtherBusinessMember