Business Segment Information (Details) - USD ($) $ in Millions	3 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Increase (decrease) in incentive stock compensation expense	$ (63)
Net sales	4,147	$ 3,816
Earnings	591	503
Operating Segments [Member] \| Automation Solutions [Member]
Segment Reporting Information [Line Items]
Net sales	2,799	2,572
Earnings	407	386
Operating Segments [Member] \| Commercial & Residential Solutions [Member]
Segment Reporting Information [Line Items]
Net sales	1,338	1,252
Earnings	237	252
Operating Segments [Member] \| Climate Technologies [Member]
Segment Reporting Information [Line Items]
Net sales	880	922
Earnings	146	165
Operating Segments [Member] \| Tools & Home Products [Member]
Segment Reporting Information [Line Items]
Net sales	458	330
Earnings	91	87
Differences in accounting methods [Member]
Segment Reporting Information [Line Items]
Earnings	59	51
Corporate and other [Member]
Segment Reporting Information [Line Items]
Earnings	(69)	(148)
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Net sales	10	(8)
Earnings	$ (43)	(38)
Pentair's Valves & Controls [Member] \| Order or Production Backlog [Member]
Segment Reporting Information [Line Items]
Backlog amortization		15
FairValueAdjustmentToInventoryOnly [Member] \| Pentair's Valves & Controls [Member]
Segment Reporting Information [Line Items]
Earnings		$ 10

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The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

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Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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