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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 | $ 41 us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent | $ 33 us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent |
Goodwill | 63 us-gaap_Goodwill | 64 us-gaap_Goodwill |
Workforce Reduction Plan [Member] | Employee Severance [Member] |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |
Expected number of positions to be reduced | 300 us-gaap_RestructuringAndRelatedCostExpectedNumberOfPositionsEliminated / us-gaap_RestructuringCostAndReserveAxis = us-gaap_EmployeeSeveranceMember / us-gaap_RestructuringPlanAxis = csx_WorkforceReductionPlanMember |  |
Restructuring charges incurred | 39 us-gaap_RestructuringAndRelatedCostIncurredCost / us-gaap_RestructuringCostAndReserveAxis = us-gaap_EmployeeSeveranceMember / us-gaap_RestructuringPlanAxis = csx_WorkforceReductionPlanMember |  |
Total expected restructuring charges | $ 45 us-gaap_RestructuringAndRelatedCostExpectedCost1 / us-gaap_RestructuringCostAndReserveAxis = us-gaap_EmployeeSeveranceMember / us-gaap_RestructuringPlanAxis = csx_WorkforceReductionPlanMember |  |

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- Definition A valuation allowance for trade and other receivables due to an Entity within one year (or the normal operating cycle, whichever is longer) that are expected to be uncollectible. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 4 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5074-111524 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.4) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Amount expected to be recognized in earnings for the specified restructuring cost. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 5 -Section P -Subsection 3, 4 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB Topic 5.P.4(b)) -URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140904-122747 + Details
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