Postretirement Benefits - Narrative (Details) - USD ($) $ in Millions	3 Months Ended						6 Months Ended
	Apr. 30, 2018	Jan. 31, 2018	Jul. 31, 2017	Apr. 30, 2017	Jan. 31, 2017	Jul. 31, 2014	Apr. 30, 2018	Apr. 30, 2017	Oct. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)							$ 2
Defined Contribution Plan, Administrative Expense							9
Defined Benefit Plan, Cost of Providing Special and Contractual Termination Benefits					$ 1
Employer contributions	$ 32			$ 24			53	$ 46
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year	81						81
Income Tax Expense (Benefit)	7			$ 6			22	10
Liability, Defined Benefit Plan, Noncurrent	2,422						2,422		$ 2,497
Defined Contribution Plan, Cost	$ 11	$ 9					$ 18	$ 16
Chatham [Member] | Facility Closing [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Postemployment Benefits, Period Expense			$ 23		$ 6	$ 14
Liability, Defined Benefit Plan, Noncurrent			$ 66