Postretirement Benefits - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Jan. 31, 2020	Jan. 31, 2019	Oct. 31, 2020	Oct. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)		$ 11
Defined Contribution Plan, Administrative Expense		142
Liabilities	$ 10,102			$ 10,640
Employer contributions	30	131
Income Tax Expense (Benefit)	(5)	$ (19)
Liability, Defined Benefit Plan, Noncurrent	2,056			$ 2,103
Defined Contribution Plan, Cost	$ 8
Scenario, Forecast [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions			$ 162