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Research and Development Costs (Tables) | 12 Months Ended
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Dec. 31, 2017
Research and Development [Abstract] |
Schedule of Research and Development Costs |
| Year Ended December 31,
(millions of dollars) | 2017 |  | 2016 |  | 2015
Gross R&D expenditures | $ | 473.1 |  |  | $ | 417.8 |  |  | $ | 386.2 |
Customer reimbursements | (65.6 | ) |  | (74.6 | ) |  | (78.8 | )
Net R&D expenditures | $ | 407.5 |  |  | $ | 343.2 |  |  | $ | 307.4 |

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