Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2011	Jul. 02, 2011
Document Information [Line Items]
Document Type	10-K
Amendment Flag	true
AmendmentDescription	This Form 10-K/A amends the Annual Report on Form 10-K of Pentair, Inc. for the fiscal year ended December 31, 2011 (the “Form 10-K”), as filed with the Securities and Exchange Commission on February 21, 2012 to revise Item 8 of the original Form 10-K. The revision relates solely to Note 18 of the Notes to the Consolidated Financial Statements, which incorrectly included the word “Unaudited” in the header of each table. The word “Unaudited” has been removed from each table header in Note 18 in this Form 10-K/A. Except as described above, no other changes have been made to the Form 10-K, and this Form 10-K/A does not modify, amend or update in any way any of the financial or other information contained in the Form 10-K. This Form 10-K/A does not reflect events that may have occurred subsequent to the filing date of the Form 10-K.
Document Period End Date	Dec. 31, 2011
Document Fiscal Year Focus	2011
Document Fiscal Period Focus	FY
Trading Symbol	PNR
Entity Registrant Name	PENTAIR INC
Entity Central Index Key	0000077360
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding	98,622,564
Entity Public Float		$ 3,886,388,296