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Related Parties and Affiliates - Narrative (Details) $ / shares in Units, shares in Millions, $ in Millions |  |  | 1 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Oct. 17, 2019 USD ($) shares | Dec. 22, 2017 USD ($) $ / shares | Dec. 31, 2017 USD ($) $ / shares | Dec. 31, 2019 USD ($) shares | Dec. 31, 2018 USD ($) shares | Dec. 31, 2017 USD ($) shares | Dec. 26, 2014 note
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Non-cash credit to income tax expense |  | $ 3,500 |  | $ 0 | $ 0 | $ 3,506 |
Effect of change in tax rate (in dollars per share) | $ / shares |  | $ 3.81 |  |  |  |  |
Number of shares repurchased (in shares) | shares |  |  |  | 48.0 | 72.0 | 39.0 |
Amount of shares repurchased |  |  |  | $ 3,373 | $ 4,671 | $ 1,970 |
Investments in Conrail |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Investments in affiliates |  |  |  |  | 943 |  |
Corporate Joint Venture | Conrail |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Difference between carrying amount and underlying equity |  |  |  | 339 |  |  |
Promissory notes executed | note |  |  |  |  |  |  | 2
Interest expense |  |  |  | 6 | $ 6 | $ 6 |
Corporate Joint Venture | Investments in Conrail | Conrail |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Investments in affiliates |  |  |  | $ 982 |  |  |
Corporate Joint Venture | Voting interest in related party which is also an equity method investment | Conrail |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Ownership percentage |  |  |  | 50.00% |  |  |
Corporate Joint Venture | Economic interest in related party which is also an equity method investment | Conrail |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Ownership percentage |  |  |  | 42.00% |  |  |
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 |  |  |  |
Affiliated Entity | TTX |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Ownership percentage |  |  |  | 20.00% |  |  |
Equity method investments |  |  |  | $ 743 |  |  |
Affiliated Entity | MR Argent Advisor LLC |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Number of shares repurchased (in shares) | shares | 4.7 |  |  |  |  |  |
Amount of shares repurchased | $ 319 |  |  |  |  |  |

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