Financial Instruments - Derivative Instruments Designated as Fair Value Hedges and Related Hedged Items (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 28, 2019	Dec. 29, 2018
OI&E
Gains/(Losses) related to derivative instruments and hedged items:
Gains/(Losses) on derivative instruments	$ (345)	$ 1,059
Gains/(Losses) related to hedged items	345	(1,059)
Foreign exchange contracts
Carrying amounts of hedged assets/(liabilities) and cumulative hedging adjustments:
Cumulative hedging adjustment increases/(decreases) included in the carrying amount hedged marketable securities	(594)
Foreign exchange contracts | Current marketable securities and non-current marketable securities
Carrying amounts of hedged assets/(liabilities) and cumulative hedging adjustments:
Carrying amount of hedged marketable securities	15,544
Foreign exchange contracts | OI&E
Gains/(Losses) related to derivative instruments and hedged items:
Gains/(Losses) on derivative instruments	(183)	402
Gains/(Losses) related to hedged items	183	(402)
Interest rate contracts
Carrying amounts of hedged assets/(liabilities) and cumulative hedging adjustments:
Cumulative hedging adjustment (increases)/decreases included in the carrying amount hedged fixed-rate debt	(418)
Interest rate contracts | Current term debt and non-current term debt
Carrying amounts of hedged assets/(liabilities) and cumulative hedging adjustments:
Carrying amount of hedged fixed-rate debt	(28,631)
Interest rate contracts | OI&E
Gains/(Losses) related to derivative instruments and hedged items:
Gains/(Losses) on derivative instruments	(162)	657
Gains/(Losses) related to hedged items	$ 162	$ (657)