Quarterly Financial Data (unaudited) - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended		3 Months Ended								12 Months Ended
	Jul. 31, 2019	Jan. 31, 2018	Dec. 31, 2019	Sep. 28, 2019	Jun. 29, 2019	Mar. 30, 2019	Dec. 31, 2018	Sep. 29, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information [Line Items]
Tax expense (benefit) on valuation allowances on the deferred tax assets of a certain foreign subsidiary			$ 32.2				$ 11.1				$ 1.2	$ (52.4)	$ (56.8)
Tax benefit on restructuring charges and various other items							8.6	$ 7.5		$ 4.1
Tax benefit on share-based compensation						$ 3.2				10.1
Net tax benefits					$ 10.6
Research and development and other tax credits				$ 28.6							40.8	9.9	26.8
Gain from deconsolidation	$ 4.0			4.0
Tax expense on increase in foreign withholding tax on certain undistributed foreign earnings										22.0	0.0	0.0	(289.7)
Tax audits and assessments							$ 15.8		$ 17.4		0.4	6.9	(1.4)
U.S. tax rate change and other tax reform items											0.0	$ 9.8	$ 42.5
Impairment loss			5.0								$ 5.0
Foreign Tax Authority
Quarterly Financial Information [Line Items]
Tax expense (benefit) on valuation allowances on the deferred tax assets of a certain foreign subsidiary					10.4	18.4				35.1
Tax benefit on restructuring charges and various other items			14.1	$ 9.1	$ 11.0	$ 15.6
U.S. tax rate change and other tax reform items								7.2
U.S.
Quarterly Financial Information [Line Items]
Tax benefits on adjustment to 2017 provisional U.S. income tax expense								$ 6.9
Lear FAWSN
Quarterly Financial Information [Line Items]
Consolidation of affiliate, revaluation gain		$ 10.0								$ 10.0
Foreign
Quarterly Financial Information [Line Items]
Curtailment gain (loss)			$ 12.9