Earnings Per Share (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended			9 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Basic earnings per share:
Net earnings attributable to BorgWarner Inc.		$ 101.1	$ 141.6	$ 379.7	$ 428.1
Weighted average shares of common stock outstanding		114,299,000	108,779,000	111,619,000	109,391,000
Earnings per share - basic		$ 0.88	$ 1.30	$ 3.40	$ 3.91
Diluted earnings per share:
Net earnings attributable to BorgWarner Inc.		101.1	141.6	379.7	428.1
Adjustment for net interest expense on convertible notes		0	5.4	5.8	16.0
Diluted net earnings attributable to BorgWarner Inc.		$ 101.1	$ 147.0	$ 385.5	$ 444.1
Weighted average shares of common stock outstanding		114,299,000	108,779,000	111,619,000	109,391,000
Effect of 3.50% convertible notes		0	11,389,000	4,429,000	11,389,000
Effect of warrant		2,208,000	5,158,000	4,507,000	5,332,000
Effect of stock-based compensation		1,992,000	2,614,000	2,016,000	2,657,000
Total dilutive effect on weighted average shares of common stock outstanding		4,200,000	19,161,000	10,952,000	19,378,000
Weighted average shares of common stock outstanding including dilutive shares		118,499,000	127,940,000	122,571,000	128,769,000
Earnings per share - diluted		$ 0.85	$ 1.15	$ 3.15	$ 3.45
Warrant Exercise Price				$ 38.61
Treasury stock received from bond hedge, shares				6,500,000
Bond Hedge Per Share Price				$ 32.82
Settlement of warrant, shares	500,000	4,400,000
Call Option [Member]
Diluted earnings per share:
Anti-dilutive securities		0	6,092,000	2,586,000	6,240,000
Senior Notes One [Member]
Diluted earnings per share:
Debt Instrument, Interest Rate, Stated Percentage		3.50%		3.50%
Debt instrument maturity period				Apr. 15, 2012