Financial Instruments - Cash, Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Millions	Mar. 31, 2018	Sep. 30, 2017	Apr. 01, 2017	Sep. 24, 2016
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	$ 270,657	$ 268,399
Unrealized Gains	274	1,278
Unrealized Losses	(3,705)	(782)
Fair Value	267,226	268,895
Cash and Cash Equivalents	45,059	20,289	$ 15,157	$ 20,484
Short-Term Marketable Securities	42,881	53,892
Long-Term Marketable Securities	179,286	194,714
Cash
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	9,934	7,982
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	9,934	7,982
Cash and Cash Equivalents	9,934	7,982
Short-Term Marketable Securities	0	0
Long-Term Marketable Securities	0	0
Level 1
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	6,542	7,333
Unrealized Gains	0	0
Unrealized Losses	(105)	(88)
Fair Value	6,437	7,245
Cash and Cash Equivalents	5,742	6,534
Short-Term Marketable Securities	695	711
Long-Term Marketable Securities	0	0
Level 1 \| Money market funds
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	5,742	6,534
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	5,742	6,534
Cash and Cash Equivalents	5,742	6,534
Short-Term Marketable Securities	0	0
Long-Term Marketable Securities	0	0
Level 1 \| Mutual funds
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	800	799
Unrealized Gains	0	0
Unrealized Losses	(105)	(88)
Fair Value	695	711
Cash and Cash Equivalents	0	0
Short-Term Marketable Securities	695	711
Long-Term Marketable Securities	0	0
Level 2
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	254,181	253,084
Unrealized Gains	274	1,278
Unrealized Losses	(3,600)	(694)
Fair Value	250,855	253,668
Cash and Cash Equivalents	29,383	5,773
Short-Term Marketable Securities	42,186	53,181
Long-Term Marketable Securities	179,286	194,714
Level 2 \| U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	56,737	55,254
Unrealized Gains	1	58
Unrealized Losses	(932)	(230)
Fair Value	55,806	55,082
Cash and Cash Equivalents	6,379	865
Short-Term Marketable Securities	9,106	17,228
Long-Term Marketable Securities	40,321	36,989
Level 2 \| U.S. agency securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	5,539	5,162
Unrealized Gains	0	2
Unrealized Losses	(39)	(9)
Fair Value	5,500	5,155
Cash and Cash Equivalents	2,837	1,439
Short-Term Marketable Securities	588	2,057
Long-Term Marketable Securities	2,075	1,659
Level 2 \| Non-U.S. government securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	8,247	7,827
Unrealized Gains	88	210
Unrealized Losses	(137)	(37)
Fair Value	8,198	8,000
Cash and Cash Equivalents	0	9
Short-Term Marketable Securities	477	123
Long-Term Marketable Securities	7,721	7,868
Level 2 \| Certificates of deposit and time deposits
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	7,266	5,832
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	7,266	5,832
Cash and Cash Equivalents	4,611	1,142
Short-Term Marketable Securities	2,021	3,918
Long-Term Marketable Securities	634	772
Level 2 \| Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	17,417	3,640
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	17,417	3,640
Cash and Cash Equivalents	15,455	2,146
Short-Term Marketable Securities	1,962	1,494
Long-Term Marketable Securities	0	0
Level 2 \| Corporate securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	138,036	152,724
Unrealized Gains	176	969
Unrealized Losses	(1,975)	(242)
Fair Value	136,237	153,451
Cash and Cash Equivalents	101	172
Short-Term Marketable Securities	27,431	27,591
Long-Term Marketable Securities	108,705	125,688
Level 2 \| Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	973	961
Unrealized Gains	0	4
Unrealized Losses	(11)	(1)
Fair Value	962	964
Cash and Cash Equivalents	0	0
Short-Term Marketable Securities	166	114
Long-Term Marketable Securities	796	850
Level 2 \| Mortgage- and asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	19,966	21,684
Unrealized Gains	9	35
Unrealized Losses	(506)	(175)
Fair Value	19,469	21,544
Cash and Cash Equivalents	0	0
Short-Term Marketable Securities	435	656
Long-Term Marketable Securities	$ 19,034	$ 20,888

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562

+ Details

Name:	us-gaap_AvailableForSaleSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesAmortizedCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in debt and equity securities categorized neither as trading securities nor held-to-maturity securities and intended be sold or mature one year or operating cycle, if longer.

+ References

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Investments in debt and equity securities which are categorized neither as held-to-maturity nor trading and which are intended to be sold or mature more than one year from the balance sheet date or operating cycle, if longer. Such securities are reported at fair value; unrealized gains (losses) related to Available-for-sale Securities are excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain (loss) of an Available-for-sale security that is designated as being hedged in a fair value hedge is recognized in earnings during the period of the hedge, as are other than temporary declines in fair value below the cost basis for investments in equity securities and debt securities that an entity intends to sell or it is more likely than not that it will be required to sell before the recovery of its amortized cost basis. Other than temporary declines in fair value below the cost basis for debt securities categorized as Available-for-sale that an entity does not intend to sell and for which it is not more likely than not that the entity will be required to sell before the recovery of its amortized cost basis are bifurcated into credit losses and losses related to all other factors. Other than temporary declines in fair value below cost basis related to credit losses are recognized in earnings, and losses related to all other factors are recognized in other comprehensive income.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26626-111562

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82887183&loc=d3e6676-107765

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3044-108585

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.1)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_CashAndCashEquivalentsAtCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_CashMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_MoneyMarketFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_MutualFundMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_ForeignGovernmentDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_BankTimeDepositsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_CommercialPaperMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: