Comprehensive Income - Change in AOCI by Component (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances as of September 30, 2017			$ 134,047
Total other comprehensive income/(loss)	$ (47)	$ (123)	(2,683)	$ (1,179)
Balances as of June 30, 2018	114,949		114,949
Cumulative Foreign Currency Translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances as of September 30, 2017			(354)
Other comprehensive income/(loss) before reclassifications			(291)
Amounts reclassified from AOCI			0
Tax effect			4
Total other comprehensive income/(loss)			(287)
Cumulative effect of change in accounting principle			(176)
Balances as of June 30, 2018	(817)		(817)
Unrealized Gains/Losses on Derivative Instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances as of September 30, 2017			(124)
Other comprehensive income/(loss) before reclassifications			230
Amounts reclassified from AOCI			1,071
Tax effect			(258)
Total other comprehensive income/(loss)			1,043
Cumulative effect of change in accounting principle			29
Balances as of June 30, 2018	948		948
Unrealized Gains/Losses on Marketable Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances as of September 30, 2017			328
Other comprehensive income/(loss) before reclassifications			(4,576)
Amounts reclassified from AOCI			(49)
Tax effect			1,186
Total other comprehensive income/(loss)			(3,439)
Cumulative effect of change in accounting principle			(131)
Balances as of June 30, 2018	(3,242)		(3,242)
Total AOCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances as of September 30, 2017			(150)
Other comprehensive income/(loss) before reclassifications			(4,637)
Amounts reclassified from AOCI			1,022
Tax effect			932
Total other comprehensive income/(loss)			(2,683)
Cumulative effect of change in accounting principle			(278)
Balances as of June 30, 2018	$ (3,111)		$ (3,111)