Other Deductions, Net (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Other deductions, net [Line Items]
Amortization of intangibles (intellectual property and customer relationships)	$ 239	$ 238	$ 211
Restructuring costs	284	95	65
Special advisory fees	13	0	0
Other	(4)	(8)	61
Other deductions, net	532	325	337
Increase (decrease) in intangibles amortization from acquisitions		46
Acquisition and divestiture related costs		(29)
Change in pension expense (income)	$ (48)	(42)
Change in gain (loss) from foreign currency transactions		$ 13
Pentair's Valves & Controls [Member]
Other deductions, net [Line Items]
Restructuring costs			19
Order or Production Backlog [Member] | Pentair's Valves & Controls [Member]
Other deductions, net [Line Items]
Amortization of intangibles (intellectual property and customer relationships)			$ 19