Summary of Information Used to Compute Diluted Net Income Per Share (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Mar. 30, 2013	Mar. 31, 2012
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Lear	$ 108.5	$ 134.1
Average common shares outstanding	94,816,752	100,315,771
Dilutive effect of common stock equivalents	1,054,352	1,613,630
Average diluted shares outstanding	95,871,104	101,929,401
Basic net income per share attributable to Lear	$ 1.14	$ 1.34
Diluted net income per share attributable to Lear	$ 1.13	$ 1.32