Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Summary of Significant Accounting Policies [Line Items]
Depreciation and amortization expense	$ 600	$ 406	$ 452
Selling and administrative expense	4,015	2,925	3,005
Shipping and Handling [Member]
Summary of Significant Accounting Policies [Line Items]
Selling and administrative expense	$ 479	$ 365	$ 401
Minimum
Summary of Significant Accounting Policies [Line Items]
Maturity period of short-term investments at the time of purchase	3 months
Minimum | Core and Developed Technology
Summary of Significant Accounting Policies [Line Items]
Finite-lived intangible assets, useful life	15 years
Minimum | Customer relationships
Summary of Significant Accounting Policies [Line Items]
Finite-lived intangible assets, useful life	10 years
Minimum | Patents, Trademarks, and Other
Summary of Significant Accounting Policies [Line Items]
Finite-lived intangible assets, useful life	1 year
Minimum | Buildings
Summary of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life	20 years
Minimum | Machinery and Equipment
Summary of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life	4 years
Minimum | Leasehold Improvements
Summary of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life	1 year
Maximum
Summary of Significant Accounting Policies [Line Items]
Maturity period of short-term investments at the time of purchase	1 year
Maximum | Core and Developed Technology
Summary of Significant Accounting Policies [Line Items]
Finite-lived intangible assets, useful life	20 years
Maximum | Customer relationships
Summary of Significant Accounting Policies [Line Items]
Finite-lived intangible assets, useful life	15 years
Maximum | Patents, Trademarks, and Other
Summary of Significant Accounting Policies [Line Items]
Finite-lived intangible assets, useful life	40 years
Maximum | Buildings
Summary of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life	45 years
Maximum | Machinery and Equipment
Summary of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life	13 years
Maximum | Leasehold Improvements
Summary of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life	20 years