Financial Instruments - Cash, Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Millions	Jun. 29, 2019	Sep. 29, 2018
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	$ 210,179	$ 241,180
Unrealized Gains	892	209
Unrealized Losses	(461)	(4,289)
Fair Value	210,610	237,100
Cash and Cash Equivalents	50,530	25,913
Short-Term Marketable Securities	44,084	40,388
Long-Term Marketable Securities	115,996	170,799
Total cash, cash equivalents and marketable securities that were restricted from general use	19,500	20,300
Level 1
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	10,558	8,882
Unrealized Gains	0	0
Unrealized Losses	0	(116)
Fair Value	10,558	8,766
Cash and Cash Equivalents	10,558	8,083
Short-Term Marketable Securities	0	683
Long-Term Marketable Securities	0	0
Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	187,546	220,723
Unrealized Gains	892	209
Unrealized Losses	(461)	(4,173)
Fair Value	187,977	216,759
Cash and Cash Equivalents	27,897	6,255
Short-Term Marketable Securities	44,084	39,705
Long-Term Marketable Securities	115,996	170,799
Cash
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	12,075	11,575
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	12,075	11,575
Cash and Cash Equivalents	12,075	11,575
Short-Term Marketable Securities	0	0
Long-Term Marketable Securities	0	0
Money market funds \| Level 1
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	10,558	8,083
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	10,558	8,083
Cash and Cash Equivalents	10,558	8,083
Short-Term Marketable Securities	0	0
Long-Term Marketable Securities	0	0
Mutual funds \| Level 1
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost		799
Unrealized Gains		0
Unrealized Losses		(116)
Fair Value		683
Cash and Cash Equivalents		0
Short-Term Marketable Securities		683
Long-Term Marketable Securities		0
U.S. Treasury securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	37,307	47,296
Unrealized Gains	22	0
Unrealized Losses	(102)	(1,202)
Fair Value	37,227	46,094
Cash and Cash Equivalents	11,116	1,613
Short-Term Marketable Securities	8,436	7,606
Long-Term Marketable Securities	17,675	36,875
U.S. agency securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	9,552	4,127
Unrealized Gains	1	0
Unrealized Losses	(5)	(48)
Fair Value	9,548	4,079
Cash and Cash Equivalents	7,711	1,732
Short-Term Marketable Securities	450	360
Long-Term Marketable Securities	1,387	1,987
Non-U.S. government securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	20,569	21,601
Unrealized Gains	272	49
Unrealized Losses	(63)	(250)
Fair Value	20,778	21,400
Cash and Cash Equivalents	636	0
Short-Term Marketable Securities	3,467	3,355
Long-Term Marketable Securities	16,675	18,045
Certificates of deposit and time deposits \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	4,838	3,074
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	4,838	3,074
Cash and Cash Equivalents	3,495	1,247
Short-Term Marketable Securities	1,273	1,330
Long-Term Marketable Securities	70	497
Commercial paper \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	5,161	2,573
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	5,161	2,573
Cash and Cash Equivalents	4,930	1,663
Short-Term Marketable Securities	231	910
Long-Term Marketable Securities	0	0
Corporate debt securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	93,896	123,001
Unrealized Gains	550	152
Unrealized Losses	(173)	(2,038)
Fair Value	94,273	121,115
Cash and Cash Equivalents	9	0
Short-Term Marketable Securities	29,027	25,162
Long-Term Marketable Securities	65,237	95,953
Municipal securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	961	946
Unrealized Gains	9	0
Unrealized Losses	(1)	(12)
Fair Value	969	934
Cash and Cash Equivalents	0	0
Short-Term Marketable Securities	65	178
Long-Term Marketable Securities	904	756
Mortgage- and asset-backed securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	15,262	18,105
Unrealized Gains	38	8
Unrealized Losses	(117)	(623)
Fair Value	15,183	17,490
Cash and Cash Equivalents	0	0
Short-Term Marketable Securities	1,135	804
Long-Term Marketable Securities	$ 14,048	$ 16,686

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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