Restructuring Costs (Details) $ in Millions	12 Months Ended
	Sep. 30, 2018 USD ($) employees	Sep. 30, 2017 USD ($) employees	Sep. 30, 2016 USD ($) employees
Restructuring Costs [Roll Forward]
Restructuring liability, beginning balance	$ 65	$ 54
Restructuring costs	65	78	$ 96
Restructuring, paid/utilized	78	67
Restructuring liability, ending balance	$ 52	$ 65	$ 54
Total number of facilities exited	6	10	19
Total number of positions eliminated | employees	1,200	1,200	1,900
Automation Solutions [Member]
Restructuring Costs [Roll Forward]
Restructuring costs	$ 41	$ 63	$ 80
Commercial & Residential Solutions [Member]
Restructuring Costs [Roll Forward]
Restructuring costs	23	12	7
Climate Technologies [Member]
Restructuring Costs [Roll Forward]
Restructuring costs	20	10	5
Tools & Home Products [Member]
Restructuring Costs [Roll Forward]
Restructuring costs	3	2	2
Severance And Benefits [Member]
Restructuring Costs [Roll Forward]
Restructuring liability, beginning balance	60	44
Restructuring costs	43	49
Restructuring, paid/utilized	57	33
Restructuring liability, ending balance	46	60	44
Lease And Other Contract Terminations [Member]
Restructuring Costs [Roll Forward]
Restructuring liability, beginning balance	4	5
Restructuring costs	3	4
Restructuring, paid/utilized	4	5
Restructuring liability, ending balance	3	4	5
Asset Write-Downs [Member]
Restructuring Costs [Roll Forward]
Restructuring liability, beginning balance	0	0
Restructuring costs	4	7
Restructuring, paid/utilized	4	7
Restructuring liability, ending balance	0	0	0
Vacant Facility And Other Shutdown Costs [Member]
Restructuring Costs [Roll Forward]
Restructuring liability, beginning balance	1	3
Restructuring costs	6	5
Restructuring, paid/utilized	4	7
Restructuring liability, ending balance	3	1	3
Start-Up And Moving Costs [Member]
Restructuring Costs [Roll Forward]
Restructuring liability, beginning balance	0	2
Restructuring costs	9	13
Restructuring, paid/utilized	9	15
Restructuring liability, ending balance	0	0	2
Corporate, Non-Segment [Member] | Corporate and other [Member]
Restructuring Costs [Roll Forward]
Restructuring costs	1	3	$ 9
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