Financial Instruments - Cash, Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Millions	Dec. 28, 2019	Sep. 28, 2019
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	$ 205,990	$ 204,977
Unrealized Gains	1,310	1,202
Unrealized Losses	(239)	(281)
Fair Value	207,061	205,898
Cash and Cash Equivalents	39,771	48,844
Current Marketable Securities	67,391	51,713
Non-Current Marketable Securities	99,899	105,341
Total cash, cash equivalents and marketable securities that were restricted from general use	19,100	18,900
Level 1
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	11,535	15,897
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	11,535	15,897
Cash and Cash Equivalents	11,535	15,897
Current Marketable Securities	0	0
Non-Current Marketable Securities	0	0
Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	183,072	176,876
Unrealized Gains	1,310	1,202
Unrealized Losses	(239)	(281)
Fair Value	184,143	177,797
Cash and Cash Equivalents	16,853	20,743
Current Marketable Securities	67,391	51,713
Non-Current Marketable Securities	99,899	105,341
Cash
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	11,383	12,204
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	11,383	12,204
Cash and Cash Equivalents	11,383	12,204
Current Marketable Securities	0	0
Non-Current Marketable Securities	0	0
Money market funds \| Level 1
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	11,535	15,897
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	11,535	15,897
Cash and Cash Equivalents	11,535	15,897
Current Marketable Securities	0	0
Non-Current Marketable Securities	0	0
U.S. Treasury securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	28,600	30,293
Unrealized Gains	29	33
Unrealized Losses	(40)	(62)
Fair Value	28,589	30,264
Cash and Cash Equivalents	3,950	6,165
Current Marketable Securities	11,069	9,817
Non-Current Marketable Securities	13,570	14,282
U.S. agency securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	8,302	9,767
Unrealized Gains	2	1
Unrealized Losses	(1)	(3)
Fair Value	8,303	9,765
Cash and Cash Equivalents	3,703	6,489
Current Marketable Securities	4,095	2,249
Non-Current Marketable Securities	505	1,027
Non-U.S. government securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	18,978	19,821
Unrealized Gains	324	337
Unrealized Losses	(92)	(50)
Fair Value	19,210	20,108
Cash and Cash Equivalents	289	749
Current Marketable Securities	2,637	3,168
Non-Current Marketable Securities	16,284	16,191
Certificates of deposit and time deposits \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	12,916	4,041
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	12,916	4,041
Cash and Cash Equivalents	4,595	2,024
Current Marketable Securities	6,777	1,922
Non-Current Marketable Securities	1,544	95
Commercial paper \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	17,823	12,433
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	17,823	12,433
Cash and Cash Equivalents	4,254	5,193
Current Marketable Securities	13,569	7,240
Non-Current Marketable Securities	0	0
Corporate debt securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	82,007	85,383
Unrealized Gains	876	756
Unrealized Losses	(37)	(92)
Fair Value	82,846	86,047
Cash and Cash Equivalents	62	123
Current Marketable Securities	27,894	26,127
Non-Current Marketable Securities	54,890	59,797
Municipal securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	971	958
Unrealized Gains	11	8
Unrealized Losses	0	(1)
Fair Value	982	965
Cash and Cash Equivalents	0	0
Current Marketable Securities	35	68
Non-Current Marketable Securities	947	897
Mortgage- and asset-backed securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	13,475	14,180
Unrealized Gains	68	67
Unrealized Losses	(69)	(73)
Fair Value	13,474	14,174
Cash and Cash Equivalents	0	0
Current Marketable Securities	1,315	1,122
Non-Current Marketable Securities	$ 12,159	$ 13,052

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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