Business Segment Information (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Net sales	$ 4,684	$ 4,456	$ 13,401	$ 12,520
Earnings	767	768	2,033	1,929
Higher (lower) acquisition and divestiture related costs	(7)		(42)
Increase (decrease) in incentive stock compensation expense	(12)		(61)
Operating Segments [Member] \| Automation Solutions [Member]
Segment Reporting Information [Line Items]
Net sales	3,025	2,870	8,834	8,213
Earnings	477	494	1,328	1,316
Operating Segments [Member] \| Commercial & Residential Solutions [Member]
Segment Reporting Information [Line Items]
Net sales	1,662	1,592	4,561	4,327
Earnings	371	387	936	988
Operating Segments [Member] \| Climate Technologies [Member]
Segment Reporting Information [Line Items]
Net sales	1,199	1,236	3,171	3,286
Earnings	278	294	650	712
Operating Segments [Member] \| Tools & Home Products [Member]
Segment Reporting Information [Line Items]
Net sales	463	356	1,390	1,041
Earnings	93	93	286	276
Differences in accounting methods [Member]
Segment Reporting Information [Line Items]
Earnings	64	57	188	163
Corporate and other [Member]
Segment Reporting Information [Line Items]
Earnings	(102)	(131)	(285)	(425)
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Net sales	(3)	(6)	6	(20)
Earnings	$ (43)	$ (39)	$ (134)	(113)
Pentair's Valves & Controls [Member] \| Order or Production Backlog [Member]
Segment Reporting Information [Line Items]
Backlog amortization				19
FairValueAdjustmentToInventoryOnly [Member] \| Pentair's Valves & Controls [Member]
Segment Reporting Information [Line Items]
Earnings				$ (10)

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