Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 28, 2019	Dec. 29, 2018
Defined Benefit Plan Disclosure [Line Items]
Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component	$ (3)	$ (25)
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service costs	103	83
Interest costs	133	145
Expected return on plan assets	(273)	(239)
Amortization of prior-year service costs	3	3
Recognized net actuarial loss	131	64
Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component	(6)	(27)
Net periodic benefit cost	97	56
Postretirement Medical Plans
Defined Benefit Plan Disclosure [Line Items]
Service costs	3	2
Interest costs	14	16
Expected return on plan assets	(14)	(14)
Amortization of prior-year service costs	0	0
Recognized net actuarial loss	3	0
Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component	3	2
Net periodic benefit cost	$ 6	$ 4