Postretirement Benefits - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Jul. 31, 2020	Jul. 31, 2019	Jul. 31, 2020	Jul. 31, 2019	Oct. 31, 2020	Oct. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	$ 2			$ 11
Defined Contribution Plan, Administrative Expense			$ 7	142
Liabilities	10,503		10,503			$ 10,640
Employer contributions					$ 5
Income Tax Expense (Benefit)	8	$ 29	10	$ 9
Liability, Defined Benefit Plan, Noncurrent	2,013		$ 2,013			$ 2,103
Defined Contribution Plan, Cost	$ 7
Forecast [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions					$ 157