Financial Instruments - Cash, Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Millions	Dec. 30, 2017	Sep. 30, 2017	Dec. 31, 2016	Sep. 24, 2016
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	$ 286,020	$ 268,399
Unrealized Gains	733	1,278
Unrealized Losses	(1,656)	(782)
Fair Value	285,097	268,895
Cash and Cash Equivalents	27,491	20,289	$ 16,371	$ 20,484
Short-Term Marketable Securities	49,662	53,892
Long-Term Marketable Securities	207,944	194,714
Cash
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	9,529	7,982
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	9,529	7,982
Cash and Cash Equivalents	9,529	7,982
Short-Term Marketable Securities	0	0
Long-Term Marketable Securities	0	0
Level 1
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	9,370	7,333
Unrealized Gains	0	0
Unrealized Losses	(92)	(88)
Fair Value	9,278	7,245
Cash and Cash Equivalents	8,570	6,534
Short-Term Marketable Securities	708	711
Long-Term Marketable Securities	0	0
Level 1 \| Money market funds
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	8,570	6,534
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	8,570	6,534
Cash and Cash Equivalents	8,570	6,534
Short-Term Marketable Securities	0	0
Long-Term Marketable Securities	0	0
Level 1 \| Mutual funds
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	800	799
Unrealized Gains	0	0
Unrealized Losses	(92)	(88)
Fair Value	708	711
Cash and Cash Equivalents	0	0
Short-Term Marketable Securities	708	711
Long-Term Marketable Securities	0	0
Level 2
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	267,121	253,084
Unrealized Gains	733	1,278
Unrealized Losses	(1,564)	(694)
Fair Value	266,290	253,668
Cash and Cash Equivalents	9,392	5,773
Short-Term Marketable Securities	48,954	53,181
Long-Term Marketable Securities	207,944	194,714
Level 2 \| U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	60,329	55,254
Unrealized Gains	4	58
Unrealized Losses	(502)	(230)
Fair Value	59,831	55,082
Cash and Cash Equivalents	2,268	865
Short-Term Marketable Securities	13,661	17,228
Long-Term Marketable Securities	43,902	36,989
Level 2 \| U.S. agency securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	5,384	5,162
Unrealized Gains	0	2
Unrealized Losses	(22)	(9)
Fair Value	5,362	5,155
Cash and Cash Equivalents	1,376	1,439
Short-Term Marketable Securities	1,980	2,057
Long-Term Marketable Securities	2,006	1,659
Level 2 \| Non-U.S. government securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	8,651	7,827
Unrealized Gains	206	210
Unrealized Losses	(60)	(37)
Fair Value	8,797	8,000
Cash and Cash Equivalents	0	9
Short-Term Marketable Securities	223	123
Long-Term Marketable Securities	8,574	7,868
Level 2 \| Certificates of deposit and time deposits
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	6,307	5,832
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	6,307	5,832
Cash and Cash Equivalents	2,237	1,142
Short-Term Marketable Securities	3,064	3,918
Long-Term Marketable Securities	1,006	772
Level 2 \| Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	5,384	3,640
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	5,384	3,640
Cash and Cash Equivalents	3,186	2,146
Short-Term Marketable Securities	2,198	1,494
Long-Term Marketable Securities	0	0
Level 2 \| Corporate securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	157,043	152,724
Unrealized Gains	506	969
Unrealized Losses	(681)	(242)
Fair Value	156,868	153,451
Cash and Cash Equivalents	325	172
Short-Term Marketable Securities	27,252	27,591
Long-Term Marketable Securities	129,291	125,688
Level 2 \| Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	971	961
Unrealized Gains	0	4
Unrealized Losses	(8)	(1)
Fair Value	963	964
Cash and Cash Equivalents	0	0
Short-Term Marketable Securities	110	114
Long-Term Marketable Securities	853	850
Level 2 \| Mortgage- and asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	23,052	21,684
Unrealized Gains	17	35
Unrealized Losses	(291)	(175)
Fair Value	22,778	21,544
Cash and Cash Equivalents	0	0
Short-Term Marketable Securities	466	656
Long-Term Marketable Securities	$ 22,312	$ 20,888

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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