Financial Instruments - Cash, Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Millions	Dec. 29, 2018	Sep. 29, 2018	Dec. 30, 2017	Sep. 30, 2017
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	$ 248,812	$ 241,180
Unrealized Gains	94	209
Unrealized Losses	(3,871)	(4,289)
Fair Value	245,035	237,100
Cash and Cash Equivalents	44,771	25,913	$ 27,491	$ 20,289
Short-Term Marketable Securities	41,656	40,388
Long-Term Marketable Securities	158,608	170,799
Total cash, cash equivalents and marketable securities that were restricted from general use	19,900	20,300
Level 1
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	7,106	8,882
Unrealized Gains	0	0
Unrealized Losses	0	(116)
Fair Value	7,106	8,766
Cash and Cash Equivalents	6,424	8,083
Short-Term Marketable Securities	682	683
Long-Term Marketable Securities	0	0
Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	232,217	220,723
Unrealized Gains	94	209
Unrealized Losses	(3,871)	(4,173)
Fair Value	228,440	216,759
Cash and Cash Equivalents	28,858	6,255
Short-Term Marketable Securities	40,974	39,705
Long-Term Marketable Securities	158,608	170,799
Cash
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	9,489	11,575
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	9,489	11,575
Cash and Cash Equivalents	9,489	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	6,424	8,083
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	6,424	8,083
Cash and Cash Equivalents	6,424	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	682	799
Unrealized Gains	0	0
Unrealized Losses	0	(116)
Fair Value	682	683
Cash and Cash Equivalents	0	0
Short-Term Marketable Securities	682	683
Long-Term Marketable Securities	0	0
U.S. Treasury securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	46,191	47,296
Unrealized Gains	6	0
Unrealized Losses	(729)	(1,202)
Fair Value	45,468	46,094
Cash and Cash Equivalents	3,923	1,613
Short-Term Marketable Securities	6,415	7,606
Long-Term Marketable Securities	35,130	36,875
U.S. agency securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	9,731	4,127
Unrealized Gains	0	0
Unrealized Losses	(31)	(48)
Fair Value	9,700	4,079
Cash and Cash Equivalents	7,552	1,732
Short-Term Marketable Securities	597	360
Long-Term Marketable Securities	1,551	1,987
Non-U.S. government securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	23,460	21,601
Unrealized Gains	48	49
Unrealized Losses	(289)	(250)
Fair Value	23,219	21,400
Cash and Cash Equivalents	1,895	0
Short-Term Marketable Securities	4,129	3,355
Long-Term Marketable Securities	17,195	18,045
Certificates of deposit and time deposits \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	5,349	3,074
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	5,349	3,074
Cash and Cash Equivalents	3,705	1,247
Short-Term Marketable Securities	1,348	1,330
Long-Term Marketable Securities	296	497
Commercial paper \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	11,953	2,573
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	11,953	2,573
Cash and Cash Equivalents	11,679	1,663
Short-Term Marketable Securities	274	910
Long-Term Marketable Securities	0	0
Corporate debt securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	117,260	123,001
Unrealized Gains	32	152
Unrealized Losses	(2,387)	(2,038)
Fair Value	114,905	121,115
Cash and Cash Equivalents	104	0
Short-Term Marketable Securities	27,134	25,162
Long-Term Marketable Securities	87,667	95,953
Municipal securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	953	946
Unrealized Gains	1	0
Unrealized Losses	(7)	(12)
Fair Value	947	934
Cash and Cash Equivalents	0	0
Short-Term Marketable Securities	187	178
Long-Term Marketable Securities	760	756
Mortgage- and asset-backed securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	17,320	18,105
Unrealized Gains	7	8
Unrealized Losses	(428)	(623)
Fair Value	16,899	17,490
Cash and Cash Equivalents	0	0
Short-Term Marketable Securities	890	804
Long-Term Marketable Securities	$ 16,009	$ 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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