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Pre-Production Costs Related to Long-Term Supply Agreements - Narrative (Details) - USD ($) $ in Millions | 9 Months Ended
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Sep. 27, 2025 | Sep. 28, 2024
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract] |  |
Capitalized pre-production E&D costs | $ 216.2 | $ 225.4
Capitalized pre-production tooling costs related to customer-owned tools | 79.4 | 113.7
Cash collected related to E&D and tooling costs | $ 343.2 | $ 287.5

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- Definition Amount of recoverable preproduction engineering and design costs related to long term supply agreements capitalized during the reporting period. + References No definition available. + Details
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Balance Type: | debit
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X
- Definition Amount of recoverable preproduction tooling costs related to long term supply agreements capitalized during the reporting period. + References No definition available. + Details
Name: | lear_PreproductionToolingCostsRelatedToLongTermSupplyArrangementsCostsCapitalized
Namespace Prefix: | lear_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Cash recoveries of preproduction engineering, design and tooling costs incurred on behalf of a customer. + References No definition available. + Details
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Namespace Prefix: | lear_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- References No definition available. + Details
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