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Summary of Significant Accounting Policies (Details) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2021 USD ($) mi depreciableAssetClass | Dec. 31, 2020 USD ($)
Property, Plant and Equipment [Line Items] |  |
Operating route miles | mi | 19,300 |
Employees covered by collective bargaining agreements | 80.00% |
Allowance for doubtful accounts | $ | $ 8 | $ 6
Approximate number of depreciable asset classes used | depreciableAssetClass | 75 |
Equipment |  |
Property, Plant and Equipment [Line Items] |  |
Depreciation studies, period | 3 years |
Roadway |  |
Property, Plant and Equipment [Line Items] |  |
Depreciation studies, period | 6 years |
Intermodal |  |
Property, Plant and Equipment [Line Items] |  |
Market groups percent of total railway operating revenues | 28.00% |
Agriculture, Forest And Consumer Products |  |
Property, Plant and Equipment [Line Items] |  |
Market groups percent of total railway operating revenues | 20.00% |
Chemicals |  |
Property, Plant and Equipment [Line Items] |  |
Market groups percent of total railway operating revenues | 18.00% |
Metals and construction |  |
Property, Plant and Equipment [Line Items] |  |
Market groups percent of total railway operating revenues | 14.00% |
Coal |  |
Property, Plant and Equipment [Line Items] |  |
Market groups percent of total railway operating revenues | 12.00% |
Automotive |  |
Property, Plant and Equipment [Line Items] |  |
Market groups percent of total railway operating revenues | 8.00% |

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