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Summary of Significant Accounting Policies - Summary of Changes in Carrying Amount of Goodwill (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017
Goodwill [Roll Forward] |  |
Beginning balance | $ 1,401.3 | $ 1,121.3
Foreign currency translation and other | (18.4) | 62.3
Ending balance | 1,405.3 | 1,401.3
Other acquisitions |  |
Goodwill [Roll Forward] |  |
Acquisitions |  | 123.3
Shanghai Lear STEC Automotive Parts Co., Ltd. (China) |  |
Goodwill [Roll Forward] |  |
Acquisitions |  | 94.4
Lear FAWSN |  |
Goodwill [Roll Forward] |  |
Acquisitions | 22.4 |
Seating |  |
Goodwill [Roll Forward] |  |
Beginning balance | 1,274.4 | 1,091.2
Foreign currency translation and other | (30.1) | 59.9
Ending balance | 1,244.3 | 1,274.4
Seating | Other acquisitions |  |
Goodwill [Roll Forward] |  |
Acquisitions |  | 123.3
Seating | Shanghai Lear STEC Automotive Parts Co., Ltd. (China) |  |
Goodwill [Roll Forward] |  |
Acquisitions |  | 0.0
Seating | Lear FAWSN |  |
Goodwill [Roll Forward] |  |
Acquisitions | 0.0 |
E-Systems |  |
Goodwill [Roll Forward] |  |
Beginning balance | 126.9 | 30.1
Foreign currency translation and other | 11.7 | 2.4
Ending balance | 161.0 | 126.9
E-Systems | Other acquisitions |  |
Goodwill [Roll Forward] |  |
Acquisitions |  | 0.0
E-Systems | Shanghai Lear STEC Automotive Parts Co., Ltd. (China) |  |
Goodwill [Roll Forward] |  |
Acquisitions |  | $ 94.4
E-Systems | Lear FAWSN |  |
Goodwill [Roll Forward] |  |
Acquisitions | $ 22.4 |

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