Comprehensive Income and Equity - Summary of Comprehensive Income and Reconciliations of Equity (Detail) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jul. 01, 2017		Jul. 02, 2016	Jul. 01, 2017		Jul. 02, 2016	Apr. 01, 2017	Dec. 31, 2016
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	$ 3,463.5		$ 3,144.4	$ 3,192.9		$ 3,017.7
Stock-based compensation transactions	19.3		18.7	(6.5)		(8.9)
Repurchase of common stock	(126.8)		(250.2)	(254.3)		(405.0)
Dividends declared to Lear Corporation stockholders	(35.3)		(22.5)	(71.0)		(45.6)
Dividends declared to noncontrolling interest holders	(15.5)		(12.8)	(32.5)		(12.8)
Consolidation of affiliate			40.0			40.0
Adoption of ASU 2016-09 (Note 11, Taxes)							$ 0.0	$ 54.5
Non-controlling interests — other			0.0			0.0
Comprehensive income:
Net income	327.0		294.5	645.5		557.0
Other comprehensive income, net of tax:
Defined benefit plan adjustments	(1.9)		1.1	(1.2)		(1.7)
Derivative instruments and hedging activities	15.9		(13.4)	68.0		(11.4)
Foreign currency translation adjustments	110.0		(43.7)	160.8		26.8
Other comprehensive income	124.0		(56.0)	227.6		13.7
Comprehensive income	451.0		238.5	873.1		570.7
Balance at end of period	3,756.2	[1]	3,156.1	3,756.2	[1]	3,156.1
Parent
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	3,331.0		3,037.6	3,057.2		2,927.4
Stock-based compensation transactions	19.3		18.7	(6.5)		(8.9)
Repurchase of common stock	(126.8)		(250.2)	(254.3)		(405.0)
Dividends declared to Lear Corporation stockholders	(35.3)		(22.5)	(71.0)		(45.6)
Adoption of ASU 2016-09 (Note 11, Taxes)							$ 0.0	$ 54.5
Non-controlling interests — other			0.0			(2.2)
Comprehensive income:
Net income	311.9		282.4	617.7		530.8
Other comprehensive income, net of tax:
Defined benefit plan adjustments	(1.9)		1.1	(1.2)		(1.7)
Derivative instruments and hedging activities	15.9		(13.4)	68.0		(11.4)
Foreign currency translation adjustments	107.8		(40.9)	157.5		29.4
Other comprehensive income	121.8		(53.2)	224.3		16.3
Comprehensive income	433.7		229.2	842.0		547.1
Balance at end of period	3,621.9		3,012.8	3,621.9		3,012.8
Noncontrolling Interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	132.5		106.8	135.7		90.3
Dividends declared to noncontrolling interest holders	(15.5)		(12.8)	(32.5)		(12.8)
Consolidation of affiliate			40.0			40.0
Non-controlling interests — other			0.0			2.2
Comprehensive income:
Net income	15.1		12.1	27.8		26.2
Other comprehensive income, net of tax:
Foreign currency translation adjustments	2.2		(2.8)	3.3		(2.6)
Other comprehensive income	2.2		(2.8)	3.3		(2.6)
Comprehensive income	17.3		9.3	31.1		23.6
Balance at end of period	$ 134.3		$ 143.3	$ 134.3		$ 143.3

[1] Unaudited.