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Investment in Affiliates and Related-Party Transactions - Equity-method Investments in Affiliates (Details) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | --- | ---
Related Party Transaction [Line Items] |  |  |  |
Total | $ 1,985 | $ 1,879 | [1] |
Corporate Joint Venture | Conrail |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Total |  | 1,025 |  | $ 982
Affiliated Entity |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Total |  | 1,985 |  | 1,879
Affiliated Entity | TTX |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Total |  | 796 |  | 743
Affiliated Entity | Other |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Total |  | $ 164 |  | $ 154
[1] | Certain prior year data has been reclassified to conform to the current presentation.

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- Definition Amount of investment in equity method investee and investment in and advance to affiliate. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.12) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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