Summary of Significant Accounting Policies - Summary of Information Used to Compute Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Net income attributable to Lear	$ 373.9	$ 158.5	$ 753.6
Redeemable noncontrolling interest adjustment	0.0	0.0	35.9
Net income available to Lear common stockholders	$ 373.9	$ 158.5	$ 789.5
Average common shares outstanding (in shares)	60,082,833	60,254,380	61,697,192
Dilutive effect of common stock equivalents (in shares)	337,651	175,582	226,336
Average diluted shares outstanding (in shares)	60,420,484	60,429,962	61,923,528
Basic net income per share available to Lear common stockholders (in dollars per share)	$ 6.22	$ 2.63	$ 12.80
Diluted net income per share available to Lear common stockholders (in dollars per share)	$ 6.19	$ 2.62	$ 12.75