Postretirement Benefits - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2019	Jul. 31, 2018	Nov. 01, 2018	Oct. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component		$ 22		$ 73
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)			$ 11	2
Defined Contribution Plan, Administrative Expense			142	9
Liabilities	$ 10,954		10,954		$ 11,074	$ 11,156
Employer contributions	9	25	140	78
Income Tax Expense (Benefit)	29	3	9	25
Liability, Defined Benefit Plan, Noncurrent	1,929		1,929			$ 2,097
Defined Contribution Plan, Cost	$ 8	$ 7	$ 28	$ 25