Comprehensive Income and Equity - Summary of Comprehensive Income and Reconciliations of Equity (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 27, 2014		Sep. 28, 2013	Sep. 27, 2014		Sep. 28, 2013	Jun. 28, 2014	Dec. 31, 2013		Jun. 29, 2013	Dec. 31, 2012
Stockholders Equity Note [Line Items]
Lear Corporation stockholders' equity	$ 3,081.9	[1]	$ 2,813.5	$ 3,081.9	[1]	$ 2,813.5	$ 3,145.8	$ 3,045.9		$ 2,669.3	$ 3,487.1
Beginning equity balance	3,221.2		2,790.3	3,149.5		3,612.2
Noncontrolling interests	73.9	[1]	106.5	73.9	[1]	106.5	75.4	103.6	[1]	121.0	125.1
Stock-based compensation transactions	14.6		14.2	31.2		36.0
Repurchase of common stock	(103.4)		0	(259.4)		(1,000.1)
Dividends declared	(16.8)		(14.2)	(50.7)		(44.8)
Dividends paid to noncontrolling interests	(10.7)		(18.6)	(17.5)		(33.4)
Stockholders' Equity, Other	0			18.0		6.6
Sale of controlling interest	0			(11.5)
Comprehensive income:
Net income	147.9		116.7	434.3		375.9
Net income attributable to Lear	140.1		112.8	410.6		358.6
Less: Net income attributable to noncontrolling interests	7.8		3.9	23.7		17.3
Other comprehensive income (loss), net of tax:
Defined benefit plan adjustments	0		1.8	0.1		5.5
Derivative instruments and hedging activities	(8.0)		(5.3)	(3.3)		(14.1)
Foreign currency translation adjustments	(89.0)		35.1	(98.9)		(10.6)
Other comprehensive income (loss)	(97.0)		31.6	(102.1)		(19.2)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(98.4)		31.4	(101.4)		(20.1)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest	1.4		0.2	(0.7)		0.9
Comprehensive income	50.9		148.3	332.2		356.7
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	41.7		144.2	309.2		338.5
Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest	9.2		4.1	23.0		18.2
Ending equity balance	3,155.8	[1]	2,920.0	3,155.8	[1]	2,920.0
Parent
Stockholders Equity Note [Line Items]
Stock-based compensation transactions	14.6		14.2	31.2		36.0
Repurchase of common stock	(103.4)		0	(259.4)		(1,000.1)
Dividends declared	(16.8)		(14.2)	(50.7)		(44.8)
Dividends paid to noncontrolling interests				0
Adjustments to Additional Paid in Capital, Other	0			5.7		(3.2)
Other comprehensive income (loss), net of tax:
Defined benefit plan adjustments	0		1.8	0.1		5.5
Derivative instruments and hedging activities	(8.0)		(5.3)	(3.3)		(14.1)
Foreign currency translation adjustments	(90.4)		34.9	(98.2)		(11.5)
Noncontrolling interest
Stockholders Equity Note [Line Items]
Dividends paid to noncontrolling interests	(10.7)		(18.6)	(17.5)		(33.4)
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests	0			(23.7)		(3.4)
Sale of controlling interest				(11.5)
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	$ 1.4		$ 0.2	$ (0.7)		$ 0.9

[1] (1) Unaudited.