Income Taxes - Additional Information (Details) $ in Millions, € in Billions				3 Months Ended			6 Months Ended
	Jan. 01, 2018	Dec. 31, 2017	Aug. 30, 2016 EUR (€) Subsidiary	Mar. 31, 2018 USD ($)	Dec. 30, 2017 USD ($)	Apr. 01, 2017 USD ($)	Mar. 31, 2018 USD ($)	Apr. 01, 2017 USD ($)	Sep. 30, 2017 USD ($)
Income Tax Contingency [Line Items]
U.S. statutory federal income tax rate	21.00%	35.00%
Income tax expense				$ 2,346		$ 3,655	$ 9,311	$ 9,944
Provision for income taxes related to the Act, provisional amount					$ 2,600
Provision for income taxes related to remeasurement of deferred tax balances, provisional amount					1,800
Provision for income taxes related to deemed repatriation tax, provisional amount					800
Deferred tax liability for unremitted foreign earnings									$ 36,400
Deferred tax liability reversal							34,235	$ (2,822)
Deemed repatriation tax payable, provisional amount					38,000
Gross unrecognized tax benefits				9,500			9,500
Unrecognized tax benefits that would affect effective tax rate, if recognized				8,200			8,200
Unrecognized tax benefits, gross interest and penalties accrued				1,500			1,500
Reasonably possible decrease in gross unrecognized tax benefits over next 12 months				3,400			3,400
Unfavorable investigation outcome, EU State Aid rules
Income Tax Contingency [Line Items]
Number of subsidiaries impacted by European Commission tax ruling | Subsidiary			2
Maximum potential loss related to European Commission tax ruling | €			€ 13
Unfavorable investigation outcome, EU State Aid rules - interest component
Income Tax Contingency [Line Items]
Maximum potential loss related to European Commission tax ruling | €			€ 1
Accumulated Other Comprehensive Income/(Loss)
Income Tax Contingency [Line Items]
Reclassification from AOCI to retained earnings, tax effects of the Act							$ (278)
Accounting Standards Update 2018-02 | Accumulated Other Comprehensive Income/(Loss)
Income Tax Contingency [Line Items]
Reclassification from AOCI to retained earnings, tax effects of the Act				(278)
Accounting Standards Update 2018-02 | Retained Earnings
Income Tax Contingency [Line Items]
Reclassification from AOCI to retained earnings, tax effects of the Act				$ 278
Tax Cuts and Jobs Act, deemed repatriation tax, related amount
Income Tax Contingency [Line Items]
Deferred tax liability reversal					36,100
Reduction of unrecognized tax benefits					$ 1,100