Acquisitions (Narrative) (Details) (USD $)	0 Months Ended	3 Months Ended		9 Months Ended										0 Months Ended		9 Months Ended
	Aug. 22, 2011	Oct. 01, 2011	Oct. 02, 2010	Oct. 01, 2011	Oct. 02, 2010	Jun. 01, 2011 Australian Fan And Motor Company [Member]	Oct. 01, 2011 Ramu, Inc. [Member]	Apr. 05, 2011 Ramu, Inc. [Member]	Oct. 01, 2011 Unico, Inc. [Member]	Dec. 23, 2010 Unico, Inc. [Member]	Oct. 01, 2011 Elco Group B.V. [Member]	Nov. 01, 2010 Elco Group B.V. [Member]	Sep. 01, 2010 Rotor B.V. [Member]	Apr. 06, 2010 CMG Engineering Group Pty, Ltd. [Member]	Aug. 22, 2011 Electrical Products Company Of A.O.Smith Corporation [Member]	Oct. 01, 2011 Electrical Products Company Of A.O.Smith Corporation [Member]
Business Acquisition [Line Items]
Business acquisition purchase price						$ 5,700,000		$ 5,300,000		$ 107,300,000		$ 27,300,000	$ 36,400,000	$ 82,600,000
Business acquisition recorded liability							16,700,000		9,200,000
Percentage of interest acquired												55.00%
Business acquisition, cash paid											11,100,000	4,600,000		76,500,000	748,700,000
Business acquisition, cash to be paid in semi-annual payments												10,700,000
Business acquisitions no of installments payment												2
Business acquisition purchase price paid in shares														6,100,000
Business acquisition consideration in shares				2,834,026	100,000									100,000	2,834,026
Sales between acquisition period		847,034,000	774,054,000	2,615,652,000	2,221,667,000											84,800,000
Acquisition-related expenses		5,600,000		16,000,000
Intangible assets	122,500,000
Intangible assets, useful lives, minimum (years)	8
Intangible assets, useful lives, maximum (years)	15
Goodwill amount estimated to be deductible for tax purposes	$ 357,233,000