Fair Value Measurements - Level 3 Reconciliation (Details) - Guarantees [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Apr. 30, 2019	Apr. 30, 2018	Apr. 30, 2019	Apr. 30, 2018
Fair Value Assets And Liablities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset (Liability) Beginning Value	$ (21)	$ (25)	$ (24)	$ (21)
Transfers out of Level 3	0	0	0	0
Issuances	(1)	(3)	1	(8)
Settlements	0	1	1	2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset (Liability) Ending Value	$ (22)	$ (27)	$ (22)	$ (27)