Composition of Certain Financial Statement Items Investment and Other Income, Net (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 29, 2020	Sep. 27, 2020	Sep. 29, 2019	Sep. 30, 2018
Investment Income, Net [Abstract]
Interest and dividend income		$ 156	$ 300	$ 611
Net gains on marketable securities		198	295	21
Net gains on other investments		108	68	83
Net gains on deferred compensation plan assets		47	9	34
Impairment losses on other investments	$ (265)	(405)	(135)	(75)
Net gains (losses) on derivative instruments		8	(14)	(27)
Equity in net losses of investees		(21)	(93)	(145)
Net (losses) gains on foreign currency transactions		(25)	11	37
Investment and other income, net		$ 66	$ 441	$ 539