Financial Instruments - Cash, Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Millions	Mar. 30, 2019	Sep. 29, 2018
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	$ 226,558	$ 241,180
Unrealized Gains	385	209
Unrealized Losses	(1,532)	(4,289)
Fair Value	225,411	237,100
Cash and Cash Equivalents	37,988	25,913
Short-Term Marketable Securities	42,104	40,388
Long-Term Marketable Securities	145,319	170,799
Total cash, cash equivalents and marketable securities that were restricted from general use	19,300	20,300
Level 1
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	8,719	8,882
Unrealized Gains	0	0
Unrealized Losses	0	(116)
Fair Value	8,719	8,766
Cash and Cash Equivalents	8,719	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	206,088	220,723
Unrealized Gains	385	209
Unrealized Losses	(1,532)	(4,173)
Fair Value	204,941	216,759
Cash and Cash Equivalents	17,518	6,255
Short-Term Marketable Securities	42,104	39,705
Long-Term Marketable Securities	145,319	170,799
Cash
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	11,751	11,575
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	11,751	11,575
Cash and Cash Equivalents	11,751	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	8,719	8,083
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	8,719	8,083
Cash and Cash Equivalents	8,719	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	48,215	47,296
Unrealized Gains	6	0
Unrealized Losses	(401)	(1,202)
Fair Value	47,820	46,094
Cash and Cash Equivalents	8,815	1,613
Short-Term Marketable Securities	6,957	7,606
Long-Term Marketable Securities	32,048	36,875
U.S. agency securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	6,458	4,127
Unrealized Gains	0	0
Unrealized Losses	(19)	(48)
Fair Value	6,439	4,079
Cash and Cash Equivalents	4,354	1,732
Short-Term Marketable Securities	526	360
Long-Term Marketable Securities	1,559	1,987
Non-U.S. government securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	21,572	21,601
Unrealized Gains	132	49
Unrealized Losses	(108)	(250)
Fair Value	21,596	21,400
Cash and Cash Equivalents	243	0
Short-Term Marketable Securities	3,992	3,355
Long-Term Marketable Securities	17,361	18,045
Certificates of deposit and time deposits \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	3,472	3,074
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	3,472	3,074
Cash and Cash Equivalents	1,980	1,247
Short-Term Marketable Securities	1,372	1,330
Long-Term Marketable Securities	120	497
Commercial paper \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	2,150	2,573
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	2,150	2,573
Cash and Cash Equivalents	2,122	1,663
Short-Term Marketable Securities	28	910
Long-Term Marketable Securities	0	0
Corporate debt securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	106,837	123,001
Unrealized Gains	228	152
Unrealized Losses	(730)	(2,038)
Fair Value	106,335	121,115
Cash and Cash Equivalents	4	0
Short-Term Marketable Securities	28,164	25,162
Long-Term Marketable Securities	78,167	95,953
Municipal securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	946	946
Unrealized Gains	4	0
Unrealized Losses	(2)	(12)
Fair Value	948	934
Cash and Cash Equivalents	0	0
Short-Term Marketable Securities	75	178
Long-Term Marketable Securities	873	756
Mortgage- and asset-backed securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	16,438	18,105
Unrealized Gains	15	8
Unrealized Losses	(272)	(623)
Fair Value	16,181	17,490
Cash and Cash Equivalents	0	0
Short-Term Marketable Securities	990	804
Long-Term Marketable Securities	$ 15,191	$ 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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