Segment Information - Sales by Product (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Total sales	$ 1,929.9	$ 1,593.6
Freight Segment
Segment Reporting Information [Line Items]
Total sales	1,301.0	915.5
Transit Segment
Segment Reporting Information [Line Items]
Total sales	628.9	678.1
Equipment | Freight Segment
Segment Reporting Information [Line Items]
Total sales	408.0	267.1
Components | Freight Segment
Segment Reporting Information [Line Items]
Total sales	220.4	295.2
Digital Electronics | Freight Segment
Segment Reporting Information [Line Items]
Total sales	173.6	121.8
Services
Segment Reporting Information [Line Items]
Total sales	339.1	159.1
Services | Freight Segment
Segment Reporting Information [Line Items]
Total sales	499.0	231.4
Original Equipment Manufacturer | Transit Segment
Segment Reporting Information [Line Items]
Total sales	287.0	327.3
Aftermarket | Transit Segment
Segment Reporting Information [Line Items]
Total sales	$ 341.9	$ 350.8