Business Segments Information (Results Of Operations By Business Segments ) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Increase (decrease) in incentive stock compensation expense									$ 106
Net sales	$ 4,888	$ 4,456	$ 4,248	$ 3,816	$ 4,435	$ 4,039	$ 3,574	$ 3,216	17,408	$ 15,264	$ 14,522
Pretax earnings (loss)									2,667	2,335	2,316
Net income (loss)									$ 2,224	$ 1,675	$ 1,619
Diluted earnings per common share	$ 0.97	$ 1.12	$ 0.76	$ 0.61	$ 0.78	$ 0.64	$ 0.45	$ 0.48	$ 3.46	$ 2.35	$ 2.52
Total Assets	$ 20,390				$ 19,589				$ 20,390	$ 19,589	$ 21,732
Automation Solutions [Member] | Measurement & Analytical Instrumentation [Member]
Segment Reporting Information [Line Items]
Net sales									3,604	3,070	3,137
Automation Solutions [Member] | Valves, Actuators & Regulators [Member]
Segment Reporting Information [Line Items]
Net sales									3,769	2,668	2,137
Automation Solutions [Member] | Industrial Solutions [Member]
Segment Reporting Information [Line Items]
Net sales									1,947	1,680	1,621
Automation Solutions [Member] | Process Control Systems & Solutions [Member]
Segment Reporting Information [Line Items]
Net sales									2,121	2,000	2,082
Operating Segments [Member] | Automation Solutions [Member]
Segment Reporting Information [Line Items]
Net sales									11,441	9,418	8,977
Pretax earnings (loss)									1,886	1,522	1,456
Total Assets	13,720				12,581				13,720	12,581	8,759
Operating Segments [Member] | Commercial & Residential Solutions [Member]
Segment Reporting Information [Line Items]
Net sales									5,982	5,857	5,555
Pretax earnings (loss)									1,352	1,358	1,286
Total Assets	4,496				3,377				4,496	3,377	3,298
Operating Segments [Member] | Climate Technologies [Member]
Segment Reporting Information [Line Items]
Net sales									4,454	4,212	3,944
Pretax earnings (loss)									972	975	902
Total Assets	2,936				2,547				2,936	2,547	2,489
Operating Segments [Member] | Tools & Home Products [Member]
Segment Reporting Information [Line Items]
Net sales									1,528	1,645	1,611
Pretax earnings (loss)									380	383	384
Total Assets	1,560				830				1,560	830	809
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Pretax earnings (loss)									218	148	189
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Pretax earnings (loss)									(630)	(528)	(427)
Corporate, Non-Segment [Member] | Corporate and other [Member]
Segment Reporting Information [Line Items]
Total Assets	$ 2,174				$ 3,631				2,174	3,631	9,675
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Net sales									(15)	(11)	(10)
Pretax earnings (loss)									(159)	(165)	(188)
Discontinued Operations, Held-for-sale [Member]
Segment Reporting Information [Line Items]
Total assets held-for-sale											$ 6,030
Total acquired businesses
Segment Reporting Information [Line Items]
Net sales									365
Pentair's Valves & Controls [Member]
Segment Reporting Information [Line Items]
Net sales										$ 600
Diluted earnings per common share										$ (0.15)
First year acquisition accounting charges [Member] | Total acquired businesses
Segment Reporting Information [Line Items]
Pretax earnings (loss)									(79)
Net income (loss)									$ (58)
Diluted earnings per common share									$ (0.09)
First year acquisition accounting charges [Member] | Pentair's Valves & Controls [Member]
Segment Reporting Information [Line Items]
Pretax earnings (loss)									$ (29)
Fair value adjustment to inventory & backlog member [Member] | Pentair's Valves & Controls [Member]
Segment Reporting Information [Line Items]
Pretax earnings (loss)										$ (93)
Net income (loss)										$ (65)
Diluted earnings per common share										$ (0.10)