Restructuring (Details) $ in Millions	3 Months Ended					12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) employee labor_union	Dec. 31, 2015 USD ($)	Sep. 27, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Agreements with Labor Unions, Number | labor_union							3
Restructuring expense	$ 45.2	$ 13.3	$ 1.3	$ 19.2	$ 6.4	$ 58.5	$ 26.9	$ 65.7
Drivetrain [Member]
Restructuring Cost and Reserve [Line Items]
Employee termination benefits, number of employees effected | employee							450
Employee termination benefits							$ 20.1	3.0
Other restructuring charges							7.9	5.2
Restructuring expense							8.2	28.0
Gustav Wahler GmbH u. Co. KG and General Partner [Member]
Restructuring Cost and Reserve [Line Items]
Employee termination benefits							11.6	9.6
Remy International Inc. [Member]
Restructuring Cost and Reserve [Line Items]
Employee termination benefits							2.0	10.1
Other restructuring charges							3.1
Restructuring expense							10.1	6.1
Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	$ 5.4					5.4	6.4	$ 29.4
Restructuring expense						6.1	10.6
Payments for Restructuring						(7.5)	(33.8)
Restructuring Reserve, Translation Adjustment						$ 0.4	0.2
Sevcon, Inc [Member]
Restructuring Cost and Reserve [Line Items]
Business acquisition, percentage of voting interests acquired	100.00%					100.00%			100.00%
Remy International Inc. [Member]
Restructuring Cost and Reserve [Line Items]
Business acquisition, percentage of voting interests acquired								100.00%
Corporate, Non-Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expense							12.5
Engine [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expense						$ 48.2
Engine [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	$ 1.3					1.3	2.7	$ 4.1
Restructuring expense						1.4	5.6
Payments for Restructuring						(2.9)	(6.9)
Restructuring Reserve, Translation Adjustment						0.1	(0.1)
Drivetrain [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expense						6.8
Drivetrain [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	$ 4.1					4.1	3.7	$ 25.3
Restructuring expense						4.7	5.0
Payments for Restructuring						(4.6)	(26.9)
Restructuring Reserve, Translation Adjustment						$ 0.3	$ 0.3