Reporting Segments and Related Information - Adjusted EBIT (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Adjusted EBIT									$ 1,515.3	$ 1,440.4	$ 1,306.9
Restructuring expense	$ 22.7	$ 5.7	$ 31.2	$ 7.5	$ 45.2	$ 13.3			67.1	58.5	26.9
Asset impairment and loss on divestiture	25.6				71.0				25.6	71.0	127.1
Asbestos-related adjustments	22.8								22.8	0.0	(48.6)
Gain on sale of building	(19.4)								(19.4)	0.0	0.0
Other postretirement income	(2.0)	(2.4)	(2.4)	(2.6)	(1.2)	(1.3)	$ (1.4)	$ (1.2)	(9.4)	(5.1)	(4.9)
Officer stock awards modification									8.3	0.0	0.0
Merger, acquisition and divestiture expense	1.0	1.6	1.0	2.2	3.6	6.4			5.8	10.0	23.7
Lease termination settlement								5.3	0.0	5.3	0.0
Intangible asset impairment									0.0	0.0	12.6
Contract expiration gain									0.0	0.0	(6.2)
Other (income) expense, net									(3.3)	2.1	0.0
Corporate, including equity in affiliates' earnings and stock-based compensation									169.6	170.3	155.3
Interest income	(2.0)	(1.5)	(1.4)	(1.5)	(1.6)	(1.3)	(1.4)	(1.5)	(6.4)	(5.8)	(6.3)
Interest expense and finance charges	13.3	14.4	14.9	16.1	16.9	17.6	18.0	18.0	58.7	70.5	84.6
Earnings before income taxes and noncontrolling interest									1,195.9	1,063.6	942.7
Provision for income taxes	19.2	66.8	30.4	94.9	338.4	79.4	76.2	86.3	211.3	580.3	306.0
Net earnings	247.6	215.9	284.3	236.8	(132.0)	194.6	221.1	199.6	984.6	483.3	636.7
Net earnings attributable to the noncontrolling interest, net of tax	17.6	12.1	12.5	11.7	14.2	9.7	9.1	10.4	53.9	43.4	41.7
Net earnings attributable to BorgWarner Inc.	$ 230.0	$ 203.8	$ 271.8	$ 225.1	$ (146.2)	$ 184.9	$ 212.0	$ 189.2	930.7	439.9	595.0
Engine [Member]
Segment Reporting Information [Line Items]
Adjusted EBIT									1,039.9	992.1	943.9
Restructuring expense									53.5	48.2
Drivetrain [Member]
Segment Reporting Information [Line Items]
Adjusted EBIT									475.4	448.3	363.0
Restructuring expense									$ 10.3	$ 6.8	$ 8.2