Acquisitions and Divestitures Narrative (Details) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 31, 2018 USD ($) $ / shares	Mar. 31, 2017 USD ($) $ / shares	Mar. 31, 2018 USD ($) $ / shares	Mar. 31, 2017 USD ($) $ / shares	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Apr. 18, 2018 USD ($)	Jan. 10, 2018 USD ($)	Dec. 01, 2017 USD ($)	Apr. 28, 2017 USD ($)
Business Acquisition & Disposal [Line Items]
Net sales	$ 4,248	$ 3,574	$ 8,064	$ 6,790
Goodwill	5,821		5,821		$ 5,821		$ 5,316
Purchase price of businesses, net of cash acquired			770	16
Proceeds from divestiture of businesses			221	0
Pretax earnings (loss)	658	565	1,161	1,029
Net income (loss)	$ 489	$ 384	$ 883	$ 754
Diluted earnings per common share | $ / shares	$ (0.76)	$ (0.45)	$ (1.37)	$ (0.93)
Textron's Tools & Test [Member]
Business Acquisition & Disposal [Line Items]
Net sales					470
Cooper-Atkins [Member]
Business Acquisition & Disposal [Line Items]
Cash paid, net of cash acquired									$ 247
Goodwill									134
Goodwill expected tax deductible amount									134
Intangibles									$ 105
Intangible assets, weighted average useful life			12 years
Pentair's Valves & Controls [Member]
Business Acquisition & Disposal [Line Items]
Cash paid, net of cash acquired											$ 2,960
Net sales							1,400
Cash acquired											$ 207
Series of Individually Immaterial Business Acquisitions [Member]
Business Acquisition & Disposal [Line Items]
Number of additional businesses acquired			3
Cooper-Atkins & Series of Individually Immaterial Business Acquisitions [Member]
Business Acquisition & Disposal [Line Items]
Net sales					70
Paradigm [Member]
Business Acquisition & Disposal [Line Items]
Cash paid, net of cash acquired										$ 505
Net sales						$ 140
Goodwill										332
Goodwill expected tax deductible amount										160
Intangibles										$ 238
Intangible assets, weighted average useful life			11 years
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | ClosetMaid [Member]
Business Acquisition & Disposal [Line Items]
Proceeds from divestiture of businesses			$ 200
Gain (loss) on divestiture of business, after tax			$ (24)
Disposal gain (loss) impact on diluted earnings per share | $ / shares			$ (0.04)
After-tax proceeds on sale of business			$ 150
Current assets held-for-sale							73
Other noncurrent assets held-for-sale							176
Accrued expenses & other liabilities held-for-sale							61
Fair Value Adjustment To Inventory & Backlog [Member] | Pentair's Valves & Controls [Member]
Business Acquisition & Disposal [Line Items]
Pretax earnings (loss)			(29)
Net income (loss)			$ (22)
Diluted earnings per common share | $ / shares			$ 0.03
Automation Solutions [Member]
Business Acquisition & Disposal [Line Items]
Goodwill	$ 5,067		$ 5,067		5,067		4,704
Automation Solutions [Member] | Series of Individually Immaterial Business Acquisitions [Member]
Business Acquisition & Disposal [Line Items]
Number of additional businesses acquired			2
Climate Technologies [Member]
Business Acquisition & Disposal [Line Items]
Goodwill	$ 696		$ 696		$ 696		$ 555
Climate Technologies [Member] | Series of Individually Immaterial Business Acquisitions [Member]
Business Acquisition & Disposal [Line Items]
Number of additional businesses acquired			1
Subsequent Event [Member] | Textron's Tools & Test [Member]
Business Acquisition & Disposal [Line Items]
Cash paid, net of cash acquired								$ 810