Earnings Per Share (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended			6 Months Ended
	Sep. 30, 2012	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Basic earnings per share:
Net earnings attributable to BorgWarner Inc.		$ 120.6	$ 162.0	$ 278.6	$ 286.5
Weighted average shares of common stock outstanding		112,139,000	108,761,000	110,280,000	109,697,000
Earnings per share - basic		$ 1.08	$ 1.49	$ 2.53	$ 2.61
Diluted earnings per share:
Net earnings attributable to BorgWarner Inc.		120.6	162.0	278.6	286.5
Adjustment for net interest expense on convertible notes		0.8	5.4	5.8	10.6
Diluted net earnings attributable to BorgWarner Inc.		$ 121.4	$ 167.4	$ 284.4	$ 297.1
Weighted average shares of common stock outstanding		112,139,000	108,761,000	110,280,000	109,697,000
Effect of 3.50% convertible notes		1,898,000	11,389,000	6,644,000	11,389,000
Effect of warrant		5,499,000	5,421,000	5,656,000	5,419,000
Effect of stock-based compensation		1,937,000	2,571,000	2,028,000	2,678,000
Total dilutive effect on weighted average shares of common stock outstanding		9,334,000	19,381,000	14,328,000	19,486,000
Weighted average shares of common stock outstanding including dilutive shares		121,473,000	128,142,000	124,608,000	129,183,000
Earnings per share - diluted		$ 1.00	$ 1.31	$ 2.28	$ 2.30
Debt Instrument, Interest Rate, Stated Percentage		3.50%		3.50%
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	2,300,000
Call Option [Member]
Diluted earnings per share:
Anti-dilutive securities		1,108,000	6,317,000	3,879,000	6,314,000