XML 34 R87.htm IDEA: XBRL DOCUMENT v2.4.1.9
(Investments and Long-term Debt) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 26, 2014
Dec. 27, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value $ 453csx_FairValueInvestmentsDisclosure $ 668csx_FairValueInvestmentsDisclosure
Certificates of Deposit and Commercial Paper [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 250csx_FairValueInvestmentsDisclosure
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Corporate Bonds [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 141csx_FairValueInvestmentsDisclosure
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Government securities [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 51csx_FairValueInvestmentsDisclosure
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Auction Rate Securities [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 11csx_FairValueInvestmentsDisclosure
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Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 453csx_FairValueInvestmentsDisclosure
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Fair Value [Member] | Less than 1 year [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 292csx_FairValueInvestmentsDisclosure
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Fair Value [Member] | 1 - 2 years [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 45csx_FairValueInvestmentsDisclosure
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Fair Value [Member] | 2 - 5 years [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 100csx_FairValueInvestmentsDisclosure
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Fair Value [Member] | Greater than 5 years [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 16csx_FairValueInvestmentsDisclosure
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Fair Value [Member] | Level 1 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 0csx_FairValueInvestmentsDisclosure
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Fair Value [Member] | Level 1 [Member] | Certificates of Deposit and Commercial Paper [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 0csx_FairValueInvestmentsDisclosure
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Fair Value [Member] | Level 1 [Member] | Corporate Bonds [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 0csx_FairValueInvestmentsDisclosure
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Fair Value [Member] | Level 1 [Member] | Government securities [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 0csx_FairValueInvestmentsDisclosure
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Fair Value [Member] | Level 1 [Member] | Auction Rate Securities [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 0csx_FairValueInvestmentsDisclosure
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Fair Value [Member] | Level 2 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 442csx_FairValueInvestmentsDisclosure
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Long-term Debt Including Current Maturities 11,042us-gaap_DebtInstrumentFairValue
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Fair Value [Member] | Level 2 [Member] | Certificates of Deposit and Commercial Paper [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 250csx_FairValueInvestmentsDisclosure
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Fair Value [Member] | Level 2 [Member] | Corporate Bonds [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 141csx_FairValueInvestmentsDisclosure
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Fair Value [Member] | Level 2 [Member] | Government securities [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 51csx_FairValueInvestmentsDisclosure
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Fair Value [Member] | Level 2 [Member] | Auction Rate Securities [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 0csx_FairValueInvestmentsDisclosure
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Fair Value [Member] | Level 3 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 11csx_FairValueInvestmentsDisclosure
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Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 0csx_FairValueInvestmentsDisclosure
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Fair Value [Member] | Level 3 [Member] | Corporate Bonds [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 0csx_FairValueInvestmentsDisclosure
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Fair Value [Member] | Level 3 [Member] | Government securities [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 0csx_FairValueInvestmentsDisclosure
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Fair Value [Member] | Level 3 [Member] | Auction Rate Securities [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 11csx_FairValueInvestmentsDisclosure
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Amortized Cost Basis [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Amortized cost basis of investments 453us-gaap_AvailableForSaleSecuritiesAmortizedCost
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Amortized Cost Basis [Member] | Level 2 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term Debt Including Current Maturities $ 9,742us-gaap_DebtInstrumentFairValue
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