Financial Instruments - Cash, Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015	Sep. 27, 2014
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	$ 268,399	$ 235,810
Unrealized Gains	1,278	2,186
Unrealized Losses	(782)	(411)
Fair Value	268,895	237,585
Cash and Cash Equivalents	20,289	20,484	$ 21,120	$ 13,844
Short-Term Marketable Securities	53,892	46,671
Long-Term Marketable Securities	194,714	170,430
Cash
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	7,982	8,601
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	7,982	8,601
Cash and Cash Equivalents	7,982	8,601
Short-Term Marketable Securities	0	0
Long-Term Marketable Securities	0	0
Level 1
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	7,333	5,073
Unrealized Gains	0	0
Unrealized Losses	(88)	(146)
Fair Value	7,245	4,927
Cash and Cash Equivalents	6,534	3,666
Short-Term Marketable Securities	711	1,261
Long-Term Marketable Securities	0	0
Level 1 \| Money market funds
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	6,534	3,666
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	6,534	3,666
Cash and Cash Equivalents	6,534	3,666
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	1,407
Unrealized Gains	0	0
Unrealized Losses	(88)	(146)
Fair Value	711	1,261
Cash and Cash Equivalents	0	0
Short-Term Marketable Securities	711	1,261
Long-Term Marketable Securities	0	0
Level 2
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	253,084	222,136
Unrealized Gains	1,278	2,186
Unrealized Losses	(694)	(265)
Fair Value	253,668	224,057
Cash and Cash Equivalents	5,773	8,217
Short-Term Marketable Securities	53,181	45,410
Long-Term Marketable Securities	194,714	170,430
Level 2 \| U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	55,254	41,697
Unrealized Gains	58	319
Unrealized Losses	(230)	(4)
Fair Value	55,082	42,012
Cash and Cash Equivalents	865	1,527
Short-Term Marketable Securities	17,228	13,492
Long-Term Marketable Securities	36,989	26,993
Level 2 \| U.S. agency securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	5,162	7,543
Unrealized Gains	2	16
Unrealized Losses	(9)	0
Fair Value	5,155	7,559
Cash and Cash Equivalents	1,439	2,762
Short-Term Marketable Securities	2,057	2,441
Long-Term Marketable Securities	1,659	2,356
Level 2 \| Non-U.S. government securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	7,827	7,609
Unrealized Gains	210	259
Unrealized Losses	(37)	(27)
Fair Value	8,000	7,841
Cash and Cash Equivalents	9	110
Short-Term Marketable Securities	123	818
Long-Term Marketable Securities	7,868	6,913
Level 2 \| Certificates of deposit and time deposits
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	5,832	6,598
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	5,832	6,598
Cash and Cash Equivalents	1,142	1,108
Short-Term Marketable Securities	3,918	3,897
Long-Term Marketable Securities	772	1,593
Level 2 \| Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	3,640	7,433
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	3,640	7,433
Cash and Cash Equivalents	2,146	2,468
Short-Term Marketable Securities	1,494	4,965
Long-Term Marketable Securities	0	0
Level 2 \| Corporate securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	152,724	131,166
Unrealized Gains	969	1,409
Unrealized Losses	(242)	(206)
Fair Value	153,451	132,369
Cash and Cash Equivalents	172	242
Short-Term Marketable Securities	27,591	19,599
Long-Term Marketable Securities	125,688	112,528
Level 2 \| Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	961	956
Unrealized Gains	4	5
Unrealized Losses	(1)	0
Fair Value	964	961
Cash and Cash Equivalents	0	0
Short-Term Marketable Securities	114	167
Long-Term Marketable Securities	850	794
Level 2 \| Mortgage- and asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	21,684	19,134
Unrealized Gains	35	178
Unrealized Losses	(175)	(28)
Fair Value	21,544	19,284
Cash and Cash Equivalents	0	0
Short-Term Marketable Securities	656	31
Long-Term Marketable Securities	$ 20,888	$ 19,253

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

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