Segment Sales Disaggregated by Major Product Line (Detail) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net sales		$ 750.9	$ 728.2	$ 765.4	$ 748.2	$ 812.5	$ 754.1	$ 833.3	$ 788.0	$ 2,992.7	$ 3,187.9	$ 2,996.7
China
Net sales										825.4	1,071.2	1,034.9
Inter-segment
Net sales										(26.6)	(30.4)	(24.4)
Operating Segments [Member] | North America
Net sales	[1]									2,083.5	2,044.7	1,904.8
Operating Segments [Member] | North America | Water Heaters And Related Parts [Member]
Net sales										1,742.6	1,757.0	1,663.0
Operating Segments [Member] | North America | Boilers And Related Parts [Member]
Net sales										199.5	200.4	183.3
Operating Segments [Member] | North America | Water Treatment Products [Member]
Net sales	[2]									141.4	87.3	58.5
Operating Segments [Member] | Rest of World [Member]
Net sales										935.8	1,173.6	1,116.3
Operating Segments [Member] | Rest of World [Member] | China
Net sales										827.2	1,070.4	1,029.4
Operating Segments [Member] | Rest of World [Member] | All Other Rest Of World [Member]
Net sales										$ 108.6	$ 103.2	$ 86.9

[1] In 2018, the Company recognized $6.7 million of restructuring and impairment expenses in connection with the move of manufacturing operations from our Renton, Washington facility to other U.S. facilities. For additional information, see Note 5 “Restructuring and Impairment Expenses.”

[2] Includes the results of Water-Right and Hague Quality Water International (Hague) from the date of acquisition of April 8, 2019 and September 5, 2017, respectively.