Financial Instruments - Cash, Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Millions	Dec. 26, 2020	Sep. 26, 2020
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	$ 192,582	$ 189,431
Unrealized Gains	3,130	2,784
Unrealized Losses	(141)	(385)
Fair Value	195,571	191,830
Cash and Cash Equivalents	36,010	38,016
Current Marketable Securities	40,816	52,927
Non-Current Marketable Securities	118,745	100,887
Total marketable securities that were restricted from general use	19,500	18,600
Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	167,541	169,487
Unrealized Gains	3,130	2,784
Unrealized Losses	(141)	(385)
Fair Value	170,530	171,886
Cash and Cash Equivalents	10,969	18,072
Current Marketable Securities	40,816	52,927
Non-Current Marketable Securities	118,745	100,887
Cash
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	18,729	17,773
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	18,729	17,773
Cash and Cash Equivalents	18,729	17,773
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	6,312	2,171
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	6,312	2,171
Cash and Cash Equivalents	6,312	2,171
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	21,939	28,439
Unrealized Gains	270	331
Unrealized Losses	(6)	0
Fair Value	22,203	28,770
Cash and Cash Equivalents	3,227	8,580
Current Marketable Securities	8,527	11,972
Non-Current Marketable Securities	10,449	8,218
U.S. agency securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	8,698	8,604
Unrealized Gains	9	8
Unrealized Losses	(1)	0
Fair Value	8,706	8,612
Cash and Cash Equivalents	1,000	2,009
Current Marketable Securities	3,319	3,078
Non-Current Marketable Securities	4,387	3,525
Non-U.S. government securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	20,185	19,361
Unrealized Gains	395	275
Unrealized Losses	(67)	(186)
Fair Value	20,513	19,450
Cash and Cash Equivalents	100	255
Current Marketable Securities	2,874	3,329
Non-Current Marketable Securities	17,539	15,866
Certificates of deposit and time deposits \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	8,002	10,399
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	8,002	10,399
Cash and Cash Equivalents	5,009	4,043
Current Marketable Securities	2,623	6,246
Non-Current Marketable Securities	370	110
Commercial paper \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	8,620	11,226
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	8,620	11,226
Cash and Cash Equivalents	1,632	3,185
Current Marketable Securities	6,988	8,041
Non-Current Marketable Securities	0	0
Corporate debt securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	83,042	76,937
Unrealized Gains	2,155	1,834
Unrealized Losses	(44)	(175)
Fair Value	85,153	78,596
Cash and Cash Equivalents	1	0
Current Marketable Securities	16,117	19,687
Non-Current Marketable Securities	69,035	58,909
Municipal securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	1,004	1,001
Unrealized Gains	20	22
Unrealized Losses	0	0
Fair Value	1,024	1,023
Cash and Cash Equivalents	0	0
Current Marketable Securities	94	139
Non-Current Marketable Securities	930	884
Mortgage- and asset-backed securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	16,051	13,520
Unrealized Gains	281	314
Unrealized Losses	(23)	(24)
Fair Value	16,309	13,810
Cash and Cash Equivalents	0	0
Current Marketable Securities	274	435
Non-Current Marketable Securities	$ 16,035	$ 13,375

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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