Segment Information - Financial Information by Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Net sales	$ 1,226.8	$ 1,210.7	$ 3,675.6	$ 3,701.9
Segment income	192.2	182.8	543.4	538.9
Water Unit [Member]
Segment Reporting Information [Line Items]
Net sales	687.3	668.3	2,123.9	2,095.7
Segment income	130.5	119.1	407.5	373.9
Electrical Unit [Member]
Segment Reporting Information [Line Items]
Net sales	540.6	543.1	1,556.0	1,608.3
Segment income	121.5	119.6	337.8	344.0
Other
Segment Reporting Information [Line Items]
Net sales	(1.1)	(0.7)	(4.3)	(2.1)
Segment income	(20.1)	(22.5)	(74.7)	(82.8)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment income	$ 231.9	$ 216.2	$ 670.6	$ 635.1