Restructuring Costs (Details) $ in Millions	12 Months Ended
	Sep. 30, 2020 USD ($) employees	Sep. 30, 2019 USD ($) employees	Sep. 30, 2018 USD ($) employees	Sep. 30, 2021 USD ($)
Restructuring Costs [Roll Forward]
Restructuring liability, beginning balance	$ 69	$ 52
Restructuring costs	284	95	$ 65
Restructuring, paid/utilized	172	78
Restructuring liability, ending balance	$ 181	$ 69	$ 52
Total number of facilities exited	6	2	6
Total number of positions eliminated | employees	5,400	1,100	1,200
Scenario, Forecast [Member] | Minimum [Member]
Restructuring Costs [Roll Forward]
Restructuring and Related Cost, Expected Cost				$ 200
Cost of sales [Member]
Restructuring Costs [Roll Forward]
Restructuring costs	$ 20
Automation Solutions [Member]
Restructuring Costs [Roll Forward]
Restructuring costs	232	$ 65	$ 41
Commercial & Residential Solutions [Member]
Restructuring Costs [Roll Forward]
Restructuring costs	44	27	23
Climate Technologies [Member]
Restructuring Costs [Roll Forward]
Restructuring costs	23	20	20
Tools & Home Products [Member]
Restructuring Costs [Roll Forward]
Restructuring costs	21	7	3
Severance And Benefits [Member]
Restructuring Costs [Roll Forward]
Restructuring liability, beginning balance	62	46
Restructuring costs	239	72
Restructuring, paid/utilized	125	56
Restructuring liability, ending balance	176	62	46
Other Restructuring [Member]
Restructuring Costs [Roll Forward]
Restructuring liability, beginning balance	7	6
Restructuring costs	45	23
Restructuring, paid/utilized	47	22
Restructuring liability, ending balance	5	7	6
Corporate, Non-Segment [Member] | Corporate and other [Member]
Restructuring Costs [Roll Forward]
Restructuring costs	$ 8	3	1
Pentair's Valves & Controls [Member]
Restructuring Costs [Roll Forward]
Restructuring costs			$ 19
Fiscal year 2019 acquired businesses and Pentair's Valves & Controls [Member]
Restructuring Costs [Roll Forward]
Restructuring costs		$ 7