Earnings Per Share - Basic and Diluted Earnings Per Share (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 28, 2015	Mar. 29, 2014
Computation Of Earnings Per Share Line Items
Net income	$ 113.9us-gaap_NetIncomeLoss	$ 118.6us-gaap_NetIncomeLoss
Income (Loss) from Continuing Operations Attributable to Parent	$ 118.2	$ 125.5
Weighted average common shares outstanding
Basic (shares)	180.1	196.2
Dilutive impact of stock options and restricted stock units (shares)	2.6	3.5
Diluted (shares)	182.7	199.7
Earnings per common share attributable to Pentair Ltd.
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.66	$ 0.64
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share	$ (0.03)	$ (0.04)
Basic (USD per share)	$ 0.63us-gaap_EarningsPerShareBasic	$ 0.60us-gaap_EarningsPerShareBasic
Income (Loss) from Continuing Operations, Per Diluted Share	$ 0.65	$ 0.63
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share	$ (0.03)	$ (0.04)
Diluted (USD per share)	$ 0.62us-gaap_EarningsPerShareDiluted	$ 0.59us-gaap_EarningsPerShareDiluted
Anti-dilutive stock options excluded from the calculation of diluted earnings per share	1.2	0.5

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Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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