Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Jun. 30, 2018
Accounting Policies [Abstract]
Basis of Presentation and Preparation	Basis of Presentation and Preparation The accompanying condensed consolidated financial statements include the accounts of the Company. Intercompany accounts and transactions have been eliminated. In the opinion of the Company’s management, the condensed consolidated financial statements reflect all adjustments, which are normal and recurring in nature, necessary for fair financial statement presentation. The preparation of these condensed consolidated financial statements in conformity with U.S. generally accepted accounting principles (“GAAP”) requires management to make estimates and assumptions that affect the amounts reported in these condensed consolidated financial statements and accompanying notes. Actual results could differ materially from those estimates. Certain prior period amounts in the condensed consolidated financial statements and accompanying notes have been reclassified to conform to the current period’s presentation. These condensed consolidated financial statements and accompanying notes should be read in conjunction with the Company’s annual consolidated financial statements and the notes thereto included in its Annual Report on Form 10-K for the fiscal year ended September 30, 2017 (the “2017 Form 10-K”).
Fiscal Period	The Company’s fiscal year is the 52- or 53-week period that ends on the last Saturday of September. The first quarter of 2018 spanned 13 weeks, whereas a 14th week was added to the first fiscal quarter of 2017, as is done every five or six years, to realign the Company’s fiscal quarters with calendar quarters. Unless otherwise stated, references to particular years, quarters, months and periods refer to the Company’s fiscal years ended in September and the associated quarters, months and periods of those fiscal years.
New Accounting Pronouncements	During the first quarter of 2018, the Company adopted the Financial Accounting Standards Board’s (the “FASB”) Accounting Standards Update (“ASU”) No. 2016-09, Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting (“ASU 2016-09”), which modified certain aspects of the accounting for share-based payment transactions, including income taxes, classification of awards and classification in the statement of cash flows. Historically, excess tax benefits or deficiencies from the Company’s equity awards were recorded as additional paid-in capital in its Condensed Consolidated Balance Sheets and were classified as a financing activity in its Condensed Consolidated Statements of Cash Flows. Beginning in 2018, the Company records any excess tax benefits or deficiencies from its equity awards as part of the provision for income taxes in its Condensed Consolidated Statements of Operations in the reporting periods in which equity vesting occurs. The Company elected to apply the cash flow classification requirements related to excess tax benefits retrospectively to all periods presented, which resulted in an increase to cash generated by operating activities in the Condensed Consolidated Statements of Cash Flows of $534 million for the nine months ended July 1, 2017. During the second quarter of 2018, the FASB issued ASU No. 2018-02, Income Statement – Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income (“ASU 2018-02”). ASU 2018-02 allows an entity to elect to reclassify the income tax effects of the Act on items within AOCI to retained earnings. The Company elected to apply the provision of ASU 2018-02 at the beginning of the second quarter of 2018 with a reclassification of net tax benefits related to cumulative foreign currency translation and unrealized gains/losses on derivative instruments and marketable securities, resulting in a $278 million decrease in AOCI and a corresponding increase in retained earnings in the Condensed Consolidated Balance Sheet.
Fair Value Measurements	Level 2 fair value estimates are based on observable inputs other than quoted prices in active markets for identical assets and liabilities, quoted prices for identical or similar assets or liabilities in inactive markets, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 1 fair value estimates are based on quoted prices in active markets for identical assets or liabilities.
Derivative Financial Instruments	The Company records all derivatives in the Condensed Consolidated Balance Sheets at fair value. The Company’s accounting treatment for these derivative instruments is based on its hedge designation. Derivative Financial Instruments The Company may use derivatives to partially offset its business exposure to foreign currency and interest rate risk on expected future cash flows, on net investments in certain foreign subsidiaries and on certain existing assets and liabilities. However, the Company may choose not to hedge certain exposures for a variety of reasons including, but not limited to, accounting considerations and the prohibitive economic cost of hedging particular exposures. There can be no assurance the hedges will offset more than a portion of the financial impact resulting from movements in foreign currency exchange or interest rates. To help protect gross margins from fluctuations in foreign currency exchange rates, certain of the Company’s subsidiaries whose functional currency is the U.S. dollar may hedge a portion of forecasted foreign currency revenue, and subsidiaries whose functional currency is not the U.S. dollar and who sell in local currencies may hedge a portion of forecasted inventory purchases not denominated in the subsidiaries’ functional currencies. The Company may enter into forward contracts, option contracts or other instruments to manage this risk and may designate these instruments as cash flow hedges. The Company generally hedges portions of its forecasted foreign currency exposure associated with revenue and inventory purchases, typically for up to 12 months. To help protect the net investment in a foreign operation from adverse changes in foreign currency exchange rates, the Company may enter into foreign currency forward and option contracts to offset the changes in the carrying amounts of these investments due to fluctuations in foreign currency exchange rates. In addition, the Company may use non-derivative financial instruments, such as its foreign currency–denominated debt, as economic hedges of its net investments in certain foreign subsidiaries. In both of these cases, the Company designates these instruments as net investment hedges. To help protect the Company’s foreign currency–denominated term debt or marketable securities from fluctuations in foreign currency exchange rates, the Company may enter into forward contracts, cross-currency swaps or other instruments. These instruments may offset a portion of the foreign currency remeasurement gains or losses, or changes in fair value. The Company may designate these instruments as either cash flow or fair value hedges. As of June 30, 2018, the Company’s hedged term debt– and marketable securities–related foreign currency transactions are expected to be recognized within 24 years. The Company may also enter into non-designated foreign currency contracts to partially offset the foreign currency exchange gains and losses generated by the remeasurement of certain assets and liabilities denominated in non-functional currencies. To help protect the Company’s foreign currency–denominated term debt or marketable securities from fluctuations in interest rates, the Company may enter into interest rate swaps, options or other instruments. These instruments may offset a portion of the changes in interest income or expense, or changes in fair value. The Company designates these instruments as either cash flow or fair value hedges. As of June 30, 2018, the Company’s hedged interest rate transactions are expected to be recognized within 9 years. Cash Flow Hedges The effective portions of cash flow hedges are recorded in accumulated other comprehensive income/(loss) (“AOCI”) until the hedged item is recognized in earnings. Deferred gains and losses associated with cash flow hedges of foreign currency revenue are recognized as a component of net sales in the same period as the related revenue is recognized, and deferred gains and losses related to cash flow hedges of inventory purchases are recognized as a component of cost of sales in the same period as the related costs are recognized. Deferred gains and losses associated with cash flow hedges of interest income or expense are recognized in other income/(expense), net in the same period as the related income or expense is recognized. The ineffective portions and amounts excluded from the effectiveness testing of cash flow hedges are recognized in other income/(expense), net. Derivative instruments designated as cash flow hedges must be de-designated as hedges when it is probable the forecasted hedged transaction will not occur in the initially identified time period or within a subsequent two-month time period. Deferred gains and losses in AOCI associated with such derivative instruments are reclassified into other income/(expense), net in the period of de-designation. Any subsequent changes in fair value of such derivative instruments are reflected in other income/(expense), net unless they are re-designated as hedges of other transactions. Net Investment Hedges The effective portions of net investment hedges are recorded in other comprehensive income/(loss) (“OCI”) as a part of the cumulative translation adjustment. The ineffective portions and amounts excluded from the effectiveness testing of net investment hedges are recognized in other income/(expense), net. Fair Value Hedges Gains and losses related to changes in fair value hedges are recognized in earnings along with a corresponding loss or gain related to the change in value of the underlying hedged item. Non-Designated Derivatives Derivatives that are not designated as hedging instruments are adjusted to fair value through earnings in the financial statement line item to which the derivative relates.
Segment Reporting	The Company reports segment information based on the “management” approach. The management approach designates the internal reporting used by management for making decisions and assessing performance as the source of the Company’s reportable segments. The Company manages its business primarily on a geographic basis. The Company’s reportable segments consist of the Americas, Europe, Greater China, Japan and Rest of Asia Pacific. Americas includes both North and South America. Europe includes European countries, as well as India, the Middle East and Africa. Greater China includes China, Hong Kong and Taiwan. Rest of Asia Pacific includes Australia and those Asian countries not included in the Company’s other reportable segments. Although the reportable segments provide similar hardware and software products and similar services, each one is managed separately to better align with the location of the Company’s customers and distribution partners and the unique market dynamics of each geographic region. The accounting policies of the various segments are the same as those described in Note 1, “Summary of Significant Accounting Policies” of the Notes to Consolidated Financial Statements in Part II, Item 8 of the 2017 Form 10-K. The Company evaluates the performance of its reportable segments based on net sales and operating income. Net sales for geographic segments are generally based on the location of customers and sales through the Company’s retail stores located in those geographic locations. Operating income for each segment includes net sales to third parties, related cost of sales and operating expenses directly attributable to the segment. Advertising expenses are generally included in the geographic segment in which the expenditures are incurred. Operating income for each segment excludes other income and expense and certain expenses managed outside the reportable segments. Costs excluded from segment operating income include various corporate expenses such as research and development, corporate marketing expenses, certain share-based compensation expenses, income taxes, various nonrecurring charges and other separately managed general and administrative costs. The Company does not include intercompany transfers between segments for management reporting purposes.