Reporting Segments (Details) (USD $) In Millions	3 Months Ended			9 Months Ended			12 Months Ended
	Sep. 30, 2011		Sep. 30, 2010	Sep. 30, 2011		Sep. 30, 2010	Dec. 31, 2008	Dec. 31, 2010
Net Sales by Reporting Segment
Segment Reporting, Entity Consolidated Revenue	$ 1,791.8		$ 1,410.9	$ 5,341.0		$ 4,119.4
Adjusted earnings before interest, income taxes and noncontrolling interest
Adjusted EBIT	198.8		123.0	606.4		346.9
Adjusted EBIT	231.7		167.5	685.9		481.0
Patent infringement settlement	0		0	(29.1)		0	(4.0)
Environmental litigation settlement	0		0	0		28.0
BERU - Eichenauer equity investment gain	0		0	0		(8.0)
Corporate, including equity in affiliates' earnings and stock-based compensation	21.4		34.0	80.6		84.3
Interest income	(1.3)		(0.6)	(3.5)		(1.8)
Interest expense and finance charges	18.5		18.4	57.4		46.8
Earnings before income taxes and noncontrolling interest	193.1		115.7	580.5		331.7
Provision for income taxes	46.4		4.2	137.1		51.1
Net earnings	146.7		111.5	443.4		280.6
Net earnings attributable to the noncontrolling interest, net of tax	5.1		4.8	15.3		14.9
Net earnings attributable to BorgWarner Inc.	141.6		106.7	428.1		265.7
Segment Reporting Information - Assets
Total assets	6,094.3			6,094.3				5,555.0
Operating Segments [Member]
Segment Reporting Information - Assets
Total assets	5,015.7			5,015.7				4,508.2
Engine [Member]
Net Sales by Reporting Segment
Segment Reporting, Entity Consolidated Revenue	1,258.2		1,018.8	3,805.5		2,942.4
Adjusted earnings before interest, income taxes and noncontrolling interest
Adjusted EBIT	188.2		136.4	571.5		375.9
Segment Reporting Information - Assets
Total assets	3,436.7			3,436.7				3,277.7
Drivetrain [Member]
Net Sales by Reporting Segment
Segment Reporting, Entity Consolidated Revenue	538.7		397.1	1,550.8		1,191.6
Adjusted earnings before interest, income taxes and noncontrolling interest
Adjusted EBIT	43.5		31.1	114.4		105.1
Segment Reporting Information - Assets
Total assets	1,579.0			1,579.0				1,230.5
Business Intersegment, Eliminations [Member]
Net Sales by Reporting Segment
Segment Reporting, Entity Consolidated Revenue	(5.1)		(5.0)	(15.3)		(14.6)
Corporate [Member]
Segment Reporting Information - Assets
Total assets	$ 1,078.6	[1]		$ 1,078.6	[1]			$ 1,046.8	[1]

[1] Corporate assets include equity in affiliates, investments and advances and deferred income taxes