Segment Information - Financial Information by Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Net sales	$ 1,269.7	$ 1,183.5
Segment income	152.3	140.6
Water Unit [Member]
Segment Reporting Information [Line Items]
Net sales	732.3	682.9
Segment income	132.7	116.1
Electrical Unit [Member]
Segment Reporting Information [Line Items]
Net sales	538.9	502.2
Segment income	106.3	104.3
Other
Segment Reporting Information [Line Items]
Net sales	(1.5)	(1.6)
Segment income	(28.5)	(34.7)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment income	$ 210.5	$ 185.7