Postretirement Benefits - Narrative (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Apr. 30, 2019	Jan. 31, 2019	Apr. 30, 2018	Apr. 30, 2019	Apr. 30, 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			$ 20		$ 51
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)				$ 11	2
Defined Contribution Plan, Administrative Expense				142	9
Liabilities	$ 10,918	$ 10,918		10,918		$ 11,074	$ 11,156
Employer contributions	0		32	131	53
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year	9			9
Income Tax Expense (Benefit)	(1)	$ (1)	7	(20)	22
Liability, Defined Benefit Plan, Noncurrent	1,950			1,950			$ 2,097
Defined Contribution Plan, Cost	$ 12		$ 11	$ 20	$ 18