Net Income Per Share Attributable to Lear (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 27, 2014	Sep. 28, 2013	Sep. 27, 2014	Sep. 28, 2013
Earnings Per Share [Abstract]
Net income attributable to Lear	$ 140.1	$ 112.8	$ 410.6	$ 358.6
Average common shares outstanding	79,974,811	80,674,338	80,652,376	86,609,304
Dilutive effect of common stock equivalents	1,428,414	1,079,825	1,374,751	1,041,134
Average diluted shares outstanding	81,403,225	81,754,163	82,027,127	87,650,438
Basic net income per share attributable to Lear	$ 1.75	$ 1.40	$ 5.09	$ 4.14
Diluted net income per share attributable to Lear	$ 1.72	$ 1.38	$ 5.01	$ 4.09