Summary of Information Used to Compute Basic and Diluted Net Income Per Share (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 29, 2012	Oct. 01, 2011	Sep. 29, 2012	Oct. 01, 2011
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Net income attributable to Lear	$ 121.4	$ 100.7	$ 400.9	$ 434.2
Average common shares outstanding	97,482,353	103,356,696	98,975,335	104,363,937
Dilutive effect of common stock equivalents	1,382,520	2,452,053	1,493,131	2,795,339
Average diluted shares outstanding	98,864,873	105,808,749	100,468,466	107,159,276
Basic net income per share attributable to Lear	$ 1.25	$ 0.97	$ 4.05	$ 4.16
Diluted net income per share attributable to Lear	$ 1.23	$ 0.95	$ 3.99	$ 4.05