Acquisitions (Schedule Of Pro Forma Financial Information) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Jan. 01, 2011	Jan. 02, 2010
Business Acquisition [Line Items]
Basic earnings per share as reported	$ 3.84	$ 3.91	$ 2.76
Diluted earnings per share as reported	$ 3.79	$ 3.84	$ 2.63
Electrical Products Company Of A.O.Smith Corporation [Member]
Business Acquisition [Line Items]
Pro forma net sales	$ 3,342.7	$ 2,943.8
Pro forma net income	$ 213.0	$ 147.6
Basic earnings per share as reported	$ 3.84	$ 3.91
Pro forma basic earnings per share	$ 5.13	$ 3.59
Diluted earnings per share as reported	$ 3.79	$ 3.84
Pro forma diluted earnings per share	$ 5.08	$ 3.54

The pro forma basic net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

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The pro forma diluted net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

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- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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+ Details

- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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