Financial Instruments - Cash, Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Millions	Jun. 30, 2018	Sep. 30, 2017	Jul. 01, 2017	Sep. 24, 2016
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	$ 247,864	$ 268,399
Unrealized Gains	179	1,278
Unrealized Losses	(4,300)	(782)
Fair Value	243,743	268,895
Cash and Cash Equivalents	31,971	20,289	$ 18,571	$ 20,484
Short-Term Marketable Securities	38,999	53,892
Long-Term Marketable Securities	172,773	194,714
Total cash, cash equivalents and marketable securities that were restricted from general use	8,800
Cash
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	9,973	7,982
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	9,973	7,982
Cash and Cash Equivalents	9,973	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	8,521	7,333
Unrealized Gains	0	0
Unrealized Losses	(112)	(88)
Fair Value	8,409	7,245
Cash and Cash Equivalents	7,722	6,534
Short-Term Marketable Securities	687	711
Long-Term Marketable Securities	0	0
Level 1 \| Money market funds
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	7,722	6,534
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	7,722	6,534
Cash and Cash Equivalents	7,722	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	799	799
Unrealized Gains	0	0
Unrealized Losses	(112)	(88)
Fair Value	687	711
Cash and Cash Equivalents	0	0
Short-Term Marketable Securities	687	711
Long-Term Marketable Securities	0	0
Level 2
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	229,370	253,084
Unrealized Gains	179	1,278
Unrealized Losses	(4,188)	(694)
Fair Value	225,361	253,668
Cash and Cash Equivalents	14,276	5,773
Short-Term Marketable Securities	38,312	53,181
Long-Term Marketable Securities	172,773	194,714
Level 2 \| U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	47,056	55,254
Unrealized Gains	1	58
Unrealized Losses	(1,055)	(230)
Fair Value	46,002	55,082
Cash and Cash Equivalents	350	865
Short-Term Marketable Securities	7,262	17,228
Long-Term Marketable Securities	38,390	36,989
Level 2 \| U.S. agency securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	6,994	5,162
Unrealized Gains	0	2
Unrealized Losses	(44)	(9)
Fair Value	6,950	5,155
Cash and Cash Equivalents	4,477	1,439
Short-Term Marketable Securities	483	2,057
Long-Term Marketable Securities	1,990	1,659
Level 2 \| Non-U.S. government securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	11,774	7,827
Unrealized Gains	40	210
Unrealized Losses	(282)	(37)
Fair Value	11,532	8,000
Cash and Cash Equivalents	0	9
Short-Term Marketable Securities	1,124	123
Long-Term Marketable Securities	10,408	7,868
Level 2 \| Certificates of deposit and time deposits
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	5,662	5,832
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	5,662	5,832
Cash and Cash Equivalents	3,649	1,142
Short-Term Marketable Securities	1,412	3,918
Long-Term Marketable Securities	601	772
Level 2 \| Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	7,064	3,640
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	7,064	3,640
Cash and Cash Equivalents	5,653	2,146
Short-Term Marketable Securities	1,411	1,494
Long-Term Marketable Securities	0	0
Level 2 \| Corporate securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	130,945	152,724
Unrealized Gains	129	969
Unrealized Losses	(2,246)	(242)
Fair Value	128,828	153,451
Cash and Cash Equivalents	147	172
Short-Term Marketable Securities	25,874	27,591
Long-Term Marketable Securities	102,807	125,688
Level 2 \| Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	956	961
Unrealized Gains	0	4
Unrealized Losses	(8)	(1)
Fair Value	948	964
Cash and Cash Equivalents	0	0
Short-Term Marketable Securities	172	114
Long-Term Marketable Securities	776	850
Level 2 \| Mortgage- and asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	18,919	21,684
Unrealized Gains	9	35
Unrealized Losses	(553)	(175)
Fair Value	18,375	21,544
Cash and Cash Equivalents	0	0
Short-Term Marketable Securities	574	656
Long-Term Marketable Securities	$ 17,801	$ 20,888

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

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