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Properties (Details) - USD ($) $ in Millions | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2021 | Dec. 31, 2020
Property, Plant and Equipment [Line Items] |  |  |
Cost |  | $ 76,488 | $ 75,420
Accumulated depreciation |  | 22,126 | 21,259
Net book value |  | 54,362 | 54,161
Land [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Cost |  | 5,283 | 5,246
Net book value |  | 5,283 | 5,246
Road: Rail and Other Track Material [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Cost |  | 17,882 | 17,620
Accumulated depreciation |  | 6,790 | 6,631
Net book value |  | $ 11,092 | $ 10,989
Estimated useful life |  | 43 years | 42 years
Road: Ties [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Cost |  | $ 11,292 | $ 11,051
Accumulated depreciation |  | 3,469 | 3,331
Net book value |  | $ 7,823 | $ 7,720
Estimated useful life |  | 34 years | 34 years
Road: Ballast [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Cost |  | $ 6,032 | $ 5,926
Accumulated depreciation |  | 1,828 | 1,753
Net book value |  | $ 4,204 | $ 4,173
Estimated useful life |  | 34 years | 34 years
Road: Other Roadway [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Cost | [1] | $ 21,294 | $ 21,030
Accumulated depreciation | [1] | 4,538 | 4,329
Net book value | [1] | $ 16,756 | $ 16,701
Estimated useful life | [1] | 49 years | 48 years
Total Road [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Cost |  | $ 56,500 | $ 55,627
Accumulated depreciation |  | 16,625 | 16,044
Net book value |  | 39,875 | 39,583
Equipment: Locomotives [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Cost |  | 9,362 | 9,375
Accumulated depreciation |  | 3,760 | 3,555
Net book value |  | $ 5,602 | $ 5,820
Estimated useful life |  | 17 years | 17 years
Equipment: Freight Cars [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Cost |  | $ 2,143 | $ 2,118
Accumulated depreciation |  | 815 | 789
Net book value |  | $ 1,328 | $ 1,329
Estimated useful life |  | 25 years | 25 years
Equipment: Work Equipment and Other [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Cost |  | $ 1,126 | $ 1,107
Accumulated depreciation |  | 392 | 351
Net book value |  | $ 734 | $ 756
Estimated useful life |  | 18 years | 18 years
Total Equipment [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Cost |  | $ 12,631 | $ 12,600
Accumulated depreciation |  | 4,967 | 4,695
Net book value |  | 7,664 | 7,905
Technology and Other [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Cost |  | 1,205 | 1,199
Accumulated depreciation |  | 534 | 520
Net book value |  | $ 671 | $ 679
Estimated useful life |  | 13 years | 13 years
Construction in Progress [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Cost |  | $ 869 | $ 748
Net book value |  | $ 869 | $ 748
[1] | Other roadway includes grading, bridges and tunnels, signals, buildings, and other road assets.

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