Postretirement Benefits - Schedule of Net Benefit (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Apr. 30, 2018	Jan. 31, 2018	Apr. 30, 2017	Apr. 30, 2018	Apr. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Cost	$ 11	$ 9		$ 18	$ 16
Employer contributions	32		$ 24	53	46
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	2		2	4	4
Interest on obligations	27		26	54	53
Amortization of cumulative loss	27		30	53	59
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	0		0	9	0
Contractual termination benefits	0		0	0	1
Premiums on pension insurance	0		4	2	8
Expected return on assets	(41)		(39)	(81)	(79)
Net postretirement benefits expense	15		23	41	46
Health and Life Insurance Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	1		2	2	3
Interest on obligations	11		12	22	24
Amortization of cumulative loss	2		5	4	11
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	0		0	0	0
Contractual termination benefits	0		0	0	0
Premiums on pension insurance	0		0	0	0
Expected return on assets	(6)		(6)	(12)	(12)
Net postretirement benefits expense	$ 8		$ 13	$ 16	$ 26