Summary of Significant Accounting Policies - Summary of Information Used to Compute Basic and Diluted Net Income Per Share (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Oct. 01, 2016	Jul. 02, 2016	Apr. 02, 2016	Dec. 31, 2015	Sep. 26, 2015	Jun. 27, 2015	Mar. 28, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Net income attributable to Lear	$ 229.9	$ 214.4	$ 282.4	$ 248.4	$ 235.3	$ 181.0	$ 181.9	$ 147.3	$ 975.1	$ 745.5	$ 672.4
Average common shares outstanding (in shares)									72,345,436	76,754,270	80,187,516
Dilutive effect of common stock equivalents (in shares)									779,513	1,012,747	1,540,963
Average diluted shares outstanding (in shares)									73,124,949	77,767,017	81,728,479
Basic net income per share attributable to Lear (in dollars per share)	$ 3.28	$ 3.01	$ 3.85	$ 3.33	$ 3.13	$ 2.37	$ 2.35	$ 1.88	$ 13.48	$ 9.71	$ 8.39
Diluted net income per share attributable to Lear (in dollars per share)	$ 3.24	$ 2.98	$ 3.82	$ 3.29	$ 3.07	$ 2.34	$ 2.33	$ 1.86	$ 13.33	$ 9.59	$ 8.23