Acquisitions And Divestitures (Narrative) (Details) $ / shares in Units, $ in Millions		3 Months Ended									12 Months Ended
	Oct. 02, 2017 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($) $ / shares	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($) $ / shares	Apr. 28, 2017 USD ($)	Jan. 29, 2015 USD ($)
Business Acquisition [Line Items]
Goodwill			$ 5,316				$ 3,909					$ 5,316	$ 3,909	$ 3,847
Purchases of businesses, net of cash acquired												2,990	132	324
Net sales			4,435	$ 4,039	$ 3,574	$ 3,216	3,932	$ 3,674	$ 3,579	$ 3,337		15,264	14,522	16,249
Net income (loss)												1,550	1,664	2,733
Restructuring Charges												78	96	138
Amortization of intangible assets												222	177	174
Intangible assets, net (excluding goodwill)			1,890				902					1,890	902
Current assets held-for-sale			73				2,200					73	2,200
Gain (loss) on divestiture of business, after tax												0	0	611
Pretax earnings												2,335	2,316	3,807
Other assets							658						658
Current liabilities held-for-sale			56				1,601					56	1,601
Deferred taxes and other noncurrent liabilities							326						326
Gains (Losses) on divestitures of businesses												0	0	1,039
Series of Individually Immaterial Business Acquisitions [Member]
Business Acquisition [Line Items]
Annualized sales													51	115
Goodwill							83						83	178
Goodwill, expected tax deductible amount							27						$ 27	$ 42
Number of businesses acquired													6	8
Purchases of businesses, net of cash acquired													$ 132	$ 324
Intangible assets, net (excluding goodwill)							50						$ 50	$ 128
Intangible assets, weighted average useful life													9 years	10 years
Pentair's Valves & Controls [Member]
Business Acquisition [Line Items]
Cash paid, net of cash acquired															$ 2,960
Cash acquired															207
Annualized sales												1,400
Goodwill															1,472
Goodwill, expected tax deductible amount			0									0
Net sales												600
Net income (loss)												$ (97)
Net earnings (loss) per share | $ / shares												$ (0.15)
Restructuring Charges												$ 25
Amortization of intangible assets												29
First year pretax acquisition charges, inventory related												74
First year pretax acquisition charges, backlog												19
First year pretax acquisition accounting charges												93
Aftertax first year acquisition accounting charges												$ 65
First year acquisition accounting charges after-tax per share | $ / shares												$ 0.10
Intangibles															$ 1,045
Intangible assets, weighted average useful life												15 years
Automation Solutions [Member]
Business Acquisition [Line Items]
Goodwill			4,704				3,160					$ 4,704	$ 3,160	$ 3,138
Restructuring Charges												$ 63	$ 80	$ 102
Automation Solutions [Member] | Series of Individually Immaterial Business Acquisitions [Member]
Business Acquisition [Line Items]
Number of businesses acquired												2	4	7
Climate Technologies [Member]
Business Acquisition [Line Items]
Goodwill			555				553					$ 555	$ 553	$ 513
Restructuring Charges												10	$ 5	20
Climate Technologies [Member] | Series of Individually Immaterial Business Acquisitions [Member]
Business Acquisition [Line Items]
Number of businesses acquired													2
Tools & Home Products [Member]
Business Acquisition [Line Items]
Goodwill			$ 57				$ 196					57	$ 196	196
Restructuring Charges												2	2	$ 11
Tools & Home Products [Member] | Series of Individually Immaterial Business Acquisitions [Member]
Business Acquisition [Line Items]
Number of businesses acquired														1
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | ClosetMaid [Member]
Business Acquisition [Line Items]
Net sales												298
Pretax earnings												$ 15
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | Power Transmission Solutions [Member]
Business Acquisition [Line Items]
Net sales														$ 189
Current assets held-for-sale																$ 182
Gain (loss) on divestiture of business, after tax														$ 532
Disposal gain impact on diluted earnings per share | $ / shares														$ 0.78
Pretax earnings														$ 21
Other assets																374
Current liabilities held-for-sale																56
Deferred taxes and other noncurrent liabilities																$ 41
Proceeds from divestitures of businesses														1,400
Gains (Losses) on divestitures of businesses														939
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | InterMetro [Member]
Business Acquisition [Line Items]
Net sales														288
Current assets held-for-sale														62
Gain (loss) on divestiture of business, after tax														$ 79
Disposal gain impact on diluted earnings per share | $ / shares														$ 0.12
Pretax earnings														$ 42
Other assets														292
Current liabilities held-for-sale														34
Deferred taxes and other noncurrent liabilities														9
Proceeds from divestitures of businesses														411
Gains (Losses) on divestitures of businesses														$ 100
Acquisition-related Costs [Member] | Pentair's Valves & Controls [Member]
Business Acquisition [Line Items]
Net income (loss)													(52)
Fair Value Adjustment To Inventory & Backlog Member [Member] | Pentair's Valves & Controls [Member]
Business Acquisition [Line Items]
Net income (loss)													$ (122)
Scenario, Forecast [Member]
Business Acquisition [Line Items]
Restructuring Charges											$ 80
Gain (loss) on divestiture of business, after tax		$ (40)
Scenario, Forecast [Member] | Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | ClosetMaid [Member]
Business Acquisition [Line Items]
After-tax proceeds on sale of business		$ 140
Subsequent Event [Member] | Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | ClosetMaid [Member]
Business Acquisition [Line Items]
Proceeds from divestitures of businesses	$ 200