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Employee Benefit Plans (Plan Assets) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended |
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Dec. 26, 2014 | Dec. 27, 2013
Defined Benefit Plan Disclosure [Line Items] |  |
Distribution of pension plan assets | $ 2,504 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets | $ 2,500 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
Equity, Percent of Total Assets | 100.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations | 100.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
Equity [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Targeted and established equity allocation (in hundredths) | 70.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_EquityMember |
Targeted allocation of total plan assets in domestic equity (in hundredths) | 42.00%csx_DefinedBenefitPlanTargetAllocationPercentageOfTotalPlanAssetsInDomesticEquity / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_EquityMember |
Targeted allocation of total plan assets in international equity (in hundredths) | 28.00%csx_DefinedBenefitPlanTargetAllocationPercentageOfTotalPlanAssetsInInternationalEquity / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_EquityMember |
Percentage within which the planned allocation is managed (in hundredths) | 3.00%csx_PercentageWithinWhichPlanAssetsInvestmentAreManaged / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_EquityMember |
Distribution of pension plan assets | 1,715 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_EquityMember | 1,619 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_EquityMember
Equity, Percent of Total Assets | 68.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_EquityMember | 65.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_EquityMember
Fixed Income Funds [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Targeted and established equity allocation (in hundredths) | 30.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_FixedIncomeFundsMember |
Distribution of pension plan assets | 740 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_FixedIncomeFundsMember | 795 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_FixedIncomeFundsMember
Equity, Percent of Total Assets | 30.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_FixedIncomeFundsMember | 32.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_FixedIncomeFundsMember
Cash and Cash Equivalents [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Distribution of pension plan assets | $ 49 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CashAndCashEquivalentsMember | $ 86 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CashAndCashEquivalentsMember
Equity, Percent of Total Assets | 2.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CashAndCashEquivalentsMember | 3.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CashAndCashEquivalentsMember

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- Definition Target allocation percentage of investments in equity securities to total plan assets in domestic equity. + References No definition available. + Details
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- Definition Target allocation percentage of investments in equity securities to total plan assets in international equity. + References No definition available. + Details
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- Definition Target allocation percentage of investments in within which plan assets investment are managed. + References No definition available. + Details
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- Definition Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 30 -Section 35 -Paragraph 50 -URI http://asc.fasb.org/extlink&oid=29635418&loc=d3e12355-114930 + Details
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- Definition Target allocation of investments of this type to total plan assets presented on a weighted average basis. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(i) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c)(i) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e2446-114920 + Details
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- Definition Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e2446-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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