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Investments in Affiliates and Other Related Party Transactions - Additional Information (Detail) - USD ($) $ in Millions			3 Months Ended								12 Months Ended
	Sep. 08, 2017	Jun. 21, 2016	Dec. 31, 2017	Sep. 30, 2017	Jul. 01, 2017	Apr. 01, 2017	Dec. 31, 2016	Oct. 01, 2016	Jul. 02, 2016	Apr. 02, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 31, 2018
Related Party Transaction [Line Items]
Redeemable noncontrolling interest			$ 153.4				$ 0.0				$ 153.4	$ 0.0
Noncontrolling interest, change in redemption value											(25.5)
Annual sales			5,363.8	$ 4,981.5	$ 5,123.2	$ 4,998.5	$ 4,643.5	$ 4,526.4	$ 4,724.8	$ 4,662.9	20,467.0	18,557.6	$ 18,211.4
Shanghai Lear STEC Automotive Parts Co., Ltd. (China)
Related Party Transaction [Line Items]
Annual sales											280.0
Shanghai Lear STEC Automotive Parts Co., Ltd. (China)
Related Party Transaction [Line Items]
Intangible assets acquired, weighted average useful life	12 years
Fair value of previously held equity interest in acquiree	$ 94.0										94.0
Noncontrolling interests, fair value	125.0
Consolidation of affiliate, revaluation gain	$ 54.2
Noncontrolling interest, ownership percentage by noncontrolling owners	45.00%
Redeemable noncontrolling interest			$ 153.4								153.4
Noncontrolling interest, change in redemption value											25.5
Beijing BAI Lear Automotive Systems Co., Ltd.
Related Party Transaction [Line Items]
Intangible assets acquired, weighted average useful life		8 years
Fair value of previously held equity interest in acquiree												$ 63.0
Noncontrolling interests, fair value		$ 41.0
Consolidation of affiliate, revaluation gain				$ 54.2					$ 30.3		$ 30.3
Equity method investment ownership interest							46.00%					46.00%	30.00%
Changchun Lear Faw Sihuan Automotive Electrical And Electronics Co Limited | Subsequent Event
Related Party Transaction [Line Items]
Equity interest acquired														20.00%

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