Business Segment Information (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Net sales	$ 4,570	$ 4,248	$ 8,717	$ 8,064
Earnings	675	658	1,266	1,161
Higher (lower) acquisition and divestiture related costs	(33)		(35)
Increase (decrease) in incentive stock compensation expense			(49)
Operating Segments [Member] \| Automation Solutions [Member]
Segment Reporting Information [Line Items]
Net sales	3,010	2,771	5,809	5,343
Earnings	444	436	851	822
Operating Segments [Member] \| Commercial & Residential Solutions [Member]
Segment Reporting Information [Line Items]
Net sales	1,561	1,483	2,899	2,735
Earnings	328	349	565	601
Operating Segments [Member] \| Climate Technologies [Member]
Segment Reporting Information [Line Items]
Net sales	1,092	1,128	1,972	2,050
Earnings	226	253	372	418
Operating Segments [Member] \| Tools & Home Products [Member]
Segment Reporting Information [Line Items]
Net sales	469	355	927	685
Earnings	102	96	193	183
Differences in accounting methods [Member]
Segment Reporting Information [Line Items]
Earnings	65	55	124	106
Corporate and other [Member]
Segment Reporting Information [Line Items]
Earnings	(114)	(146)	(183)	(294)
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Net sales	(1)	(6)	9	(14)
Earnings	$ (48)	(36)	$ (91)	(74)
Pentair's Valves & Controls [Member] \| Order or Production Backlog [Member]
Segment Reporting Information [Line Items]
Backlog amortization		$ 4		19
FairValueAdjustmentToInventoryOnly [Member] \| Pentair's Valves & Controls [Member]
Segment Reporting Information [Line Items]
Earnings				$ 10

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