Acquisitions and Divestitures Pro Forma Financial Information (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Business Acquisition [Line Items]
Net income (loss)	$ 2,328	$ 2,224	$ 1,550
Pretax earnings (loss)	$ 2,859	2,667	2,335
Net sales		18,186	17,148
Net earnings from continuing operations common stockholders		$ 2,269	$ 1,638
Diluted earnings per share from continuing operations		$ 3.56	$ 2.53
Current year acquired businesses and Pentair's Valves & Controls [Member] | Acquisition-related costs and first year acquisition accounting charges [Member] [Member]
Business Acquisition [Line Items]
Pretax earnings (loss)		$ (102)
Total acquired businesses
Business Acquisition [Line Items]
Net income (loss)		(3)
Total acquired businesses | Acquisition-related costs and first year acquisition accounting charges [Member] [Member]
Business Acquisition [Line Items]
Pretax earnings (loss)		(73)
Pentair's Valves & Controls [Member]
Business Acquisition [Line Items]
Net income (loss)			$ (97)
Pentair's Valves & Controls [Member] | Fair value adjustment to inventory & backlog member [Member]
Business Acquisition [Line Items]
Pretax earnings (loss)			(93)
Pentair's Valves & Controls [Member] | First year acquisition accounting charges [Member]
Business Acquisition [Line Items]
Pretax earnings (loss)		$ (29)
Pentair's Valves & Controls [Member] | Acquisition-related Costs [Member]
Business Acquisition [Line Items]
Pretax earnings (loss)			$ (52)