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Related Parties and Affiliates - Narrative (Details) $ / shares in Units, $ in Millions |  | 12 Months Ended
--- | --- | ---
Dec. 22, 2017 USD ($) $ / shares | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Dec. 30, 2016 USD ($) | Dec. 26, 2014 note
Related Party Transaction [Line Items] |  |  |  |  |
Non-cash credit to income tax expense | $ (3,500) | $ 0 | $ (3,506) | $ 0 |
Effect of change in tax rate (in dollars per share) | $ / shares | $ (3.81) |  |  |  |
Affiliated Entity |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |
Non-cash credit to income tax expense | $ (142) |  |  |  |
Effect of change in tax rate (in dollars per share) | $ / shares | $ (0.10) |  |  |  |
Investments in Conrail |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |
Investments in affiliates |  | 943 | 907 |  |
Corporate Joint Venture |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |
Difference between carrying amount and underlying equity |  | 343 |  |  |
Promissory notes executed | note |  |  |  |  | 2
Interest expense |  | $ 6 | $ 6 | $ 6 |
TTX Company |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |
Ownership percentage |  | 20.00% |  |  |
Equity method investments |  | $ 688 |  |  |
Voting interest in related party which is also an equity method investment | Corporate Joint Venture |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |
Ownership percentage |  | 50.00% |  |  |
Economic interest in related party which is also an equity method investment | Corporate Joint Venture |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |
Ownership percentage |  | 42.00% |  |  |

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