Restructuring Costs (Details) $ in Millions	12 Months Ended
	Sep. 30, 2019 USD ($) employees	Sep. 30, 2018 USD ($) employees	Sep. 30, 2017 USD ($) employees
Restructuring Costs [Roll Forward]
Restructuring liability, beginning balance	$ 52	$ 65
Restructuring costs	95	65	$ 78
Restructuring, paid/utilized	78	78
Restructuring liability, ending balance	$ 69	$ 52	$ 65
Total number of facilities exited	2	6	10
Total number of positions eliminated | employees	1,100	1,200	1,200
Automation Solutions [Member]
Restructuring Costs [Roll Forward]
Restructuring costs	$ 65	$ 41	$ 63
Commercial & Residential Solutions [Member]
Restructuring Costs [Roll Forward]
Restructuring costs	27	23	12
Climate Technologies [Member]
Restructuring Costs [Roll Forward]
Restructuring costs	20	20	10
Tools & Home Products [Member]
Restructuring Costs [Roll Forward]
Restructuring costs	7	3	2
Severance And Benefits [Member]
Restructuring Costs [Roll Forward]
Restructuring liability, beginning balance	46	60
Restructuring costs	72	43
Restructuring, paid/utilized	56	57
Restructuring liability, ending balance	62	46	60
Other Restructuring [Member]
Restructuring Costs [Roll Forward]
Restructuring liability, beginning balance	6	5
Restructuring costs	23	22
Restructuring, paid/utilized	22	21
Restructuring liability, ending balance	7	6	5
Corporate, Non-Segment [Member] | Corporate and other [Member]
Restructuring Costs [Roll Forward]
Restructuring costs	3	1	3
Series of Individually Immaterial Business Acquisitions [Member]
Restructuring Costs [Roll Forward]
Restructuring costs	$ 7
Current year acquired businesses and Pentair's Valves & Controls [Member]
Restructuring Costs [Roll Forward]
Restructuring costs		$ 19
Pentair's Valves & Controls [Member]
Restructuring Costs [Roll Forward]
Restructuring costs			$ 25