Segment Information - Financial Information By Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net sales	$ 1,260.9	$ 1,226.8	$ 1,265.3	$ 1,183.5	$ 1,188.1	$ 1,210.7	$ 1,301.2	$ 1,190.0	$ 4,936.5	$ 4,890.0	$ 4,616.4
Segment income (loss)											755.2
Identifiable assets (1)	8,633.7				11,534.8				8,633.7	11,534.8	11,833.5
Depreciation									85.2	84.6	81.2
Capital expenditures									70.9	117.8	91.3
Operating Income (Loss)	137.4	$ 192.2	$ 212.8	$ 138.4	161.8	$ 182.8	$ 203.4	$ 152.7	680.8	700.7	616.1
Water Quality Systems [Member]
Segment Reporting Information [Line Items]
Capital expenditures									36.1	40.8	41.5
Flow & Filtration Solutions [Member]
Segment Reporting Information [Line Items]
Capital expenditures									31.8	74.5	47.4
Water
Segment Reporting Information [Line Items]
Net sales									2,844.4	2,777.7	2,808.3
Segment income (loss)											469.0
Identifiable assets (1)	3,667.1				3,465.5				3,667.1	3,465.5	3,624.5
Depreciation									45.6	46.8	45.3
Operating Income (Loss)									546.0	494.0
Electrical
Segment Reporting Information [Line Items]
Net sales									2,097.9	2,116.0	1,809.3
Segment income (loss)											395.0
Identifiable assets (1)	4,634.1				4,419.3				4,634.1	4,419.3	4,488.4
Depreciation									34.3	31.6	27.6
Operating Income (Loss)									447.0	447.2
All Other Segments
Segment Reporting Information [Line Items]
Net sales									(5.8)	(3.7)	(1.2)
Segment income (loss)											(108.8)
Identifiable assets (1)	$ 332.5				$ 3,650.0				332.5	3,650.0	3,720.6
Depreciation									5.3	6.2	8.3
Capital expenditures									3.0	2.5	$ 2.4
Operating Income (Loss)									(95.8)	(101.7)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)									$ 897.2	$ 839.5