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Summary of Significant Accounting Policies (Tables) | 12 Months Ended
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Dec. 31, 2018
Summary of Significant Accounting Policies |
Summary of the impact of revisions in risk-free discount rate | The following table summarizes the impacts of revisions in the risk-free discount rate applied to our environmental remediation liabilities and recovery assets for the years ended December 31 (in millions) and the risk-free discount rate applied as of December 31:
|  | 2018 |  | 2017 |  | 2016 |
Decrease in operating expenses |  | $ | (2) |  | $ | — |  | $ | (2) |
Risk-free discount rate applied to environmental remediation liabilities and recovery assets |  |  | 2.75 | % |  | 2.5 | % |  | 2.5 | %
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 | The following table summarizes our investments in unconsolidated entities as of December 31 (in millions):
|  | 2018 |  | 2017
Equity method investments |  | $ | 257 |  | $ | 127
Investments without readily determinable fair values |  |  | 83 |  |  | 87
Redeemable preferred stock |  |  | 66 |  |  | 55
Investments in unconsolidated entities |  | $ | 406 |  | $ | 269
Schedule of Supplemental Cash Flow Information | The following table shows supplemental cash flow information for the years ended December 31 (in millions):
|  | 2018 |  | 2017 |  | 2016
Interest, net of capitalized interest |  | $ | 339 |  | $ | 380 |  | $ | 375
Income taxes |  |  | 349 |  |  | 562 |  |  | 442

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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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