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Summary of Significant Accounting Policies (Tables) | 12 Months Ended
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Dec. 31, 2020
Summary of Significant Accounting Policies |
Accounts Receivable, Allowance for Credit Loss [Table Text Block] | The following table reflects the activity in our allowance for doubtful accounts of trade receivables for the year ended December 31 (in millions):
​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | 2020 |  | 2019
Balance as of January 1, | ​ | $ | 28 | ​ | $ | 29
Adoption of new accounting standard | ​ |  | (1) | ​ |  | —
Additions charged to expense | ​ |  | 51 | ​ |  | 39
Accounts written-off, net of recoveries | ​ |  | (44) | ​ |  | (43)
Acquisitions, divestitures and other, net | ​ |  | (1) | ​ |  | 3
Balance as of December 31, | ​ | $ | 33 | ​ | $ | 28
Summary of the impact of revisions in risk-free discount rate | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | 2020 |  | 2019 |  | 2018 | ​
Increase (decrease) in operating expenses | ​ | $ | 8 | ​ | $ | 9 | ​ | $ | (2) | ​
Risk-free discount rate applied to environmental remediation liabilities and recovery assets | ​ |  | 1.00 | % |  | 1.75 | % |  | 2.75 | %
Schedule of estimated useful lives | The estimated useful lives for significant property and equipment categories are as follows (in years):
​ | ​ | ​
​ |  | Useful Lives
Vehicles — excluding rail haul cars |  | 3 to 10
Vehicles — rail haul cars |  | 10 to 30
Machinery and equipment — including containers |  | 3 to 30
Buildings and improvements |  | 5 to 40
Furniture, fixtures and office equipment |  | 3 to 10
Summary of investments in unconsolidated entities | ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | 2020 |  | 2019
Equity method investments | ​ | $ | 314 | ​ | $ | 377
Investments without readily determinable fair values | ​ |  | 63 | ​ | ​ | 57
Redeemable preferred stock | ​ |  | 49 | ​ | ​ | 49
Investments in unconsolidated entities | ​ | $ | 426 | ​ | $ | 483
Schedule of Supplemental Cash Flow Information | The following table shows supplemental cash flow information for the year ended December 31 (in millions):
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | 2020 |  | 2019 |  | 2018
Interest, net of capitalized interest | ​ | $ | 461 | ​ | $ | 397 | ​ | $ | 339
Income taxes | ​ |  | 422 | ​ |  | 292 | ​ |  | 349

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- Definition Tabular disclosure of allowance for credit loss on accounts receivable. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447 + Details
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- Definition A tabular presentation of the information summarizing investments in and advances to majority-owned subsidiaries, other controlled companies, and other affiliates, as prescribed by the SEC. It reflects specified information about ownership, financial results from, and financial position in such entities. Includes the tabular presentations that disaggregate investments in and advances to majority-owned subsidiaries, other controlled companies, and other affiliates. + References No definition available. + Details
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- Definition Impacts of revisions in the risk free discount rate applied to environmental remediation liabilities and recovery assets. + References No definition available. + Details
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