Net Income Per Share Attributable to Lear (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jul. 01, 2017	Jul. 02, 2016	Jul. 01, 2017	Jul. 02, 2016
Earnings Per Share [Abstract]
Net income attributable to Lear	$ 311.9	$ 282.4	$ 617.7	$ 530.8
Average common shares outstanding (in shares)	68,903,958	73,322,857	69,281,163	74,013,593
Dilutive effect of common stock equivalents (in shares)	544,840	541,600	606,910	664,554
Average diluted shares outstanding (in shares)	69,448,798	73,864,457	69,888,073	74,678,147
Basic net income per share attributable to Lear (in dollars per share)	$ 4.53	$ 3.85	$ 8.92	$ 7.17
Diluted net income per share attributable to Lear (in dollars per share)	$ 4.49	$ 3.82	$ 8.84	$ 7.11