Net Income (Loss) Per Share Attributable to Lear (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Oct. 02, 2021	Oct. 03, 2020	Oct. 02, 2021	Oct. 03, 2020
Earnings Per Share [Abstract]
Net income (loss) available to Lear	$ (26.5)	$ 174.4	$ 352.4	$ (43.1)
Average common shares outstanding (in shares)	59,906,531	60,159,356	60,171,402	60,260,886
Dilutive effect of common stock equivalents (in shares)	0	171,585	291,999	0
Average diluted shares outstanding (in shares)	59,906,531	60,330,941	60,463,401	60,260,886
Basic net income (loss) per share available to Lear common stockholders (in dollars per share)	$ (0.44)	$ 2.90	$ 5.86	$ (0.72)
Diluted net income (loss) per share available to Lear common stockholders (in dollars per share)	$ (0.44)	$ 2.89	$ 5.83	$ (0.72)