Income Taxes - Narrative (Details) - USD ($)	3 Months Ended				9 Months Ended
	Jul. 31, 2018	Jan. 31, 2018	Jul. 31, 2017	Jan. 31, 2017	Jul. 31, 2018	Jul. 31, 2017
Operating Loss Carryforwards [Line Items]
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount		$ 0.21		$ 0.35
Deferred Tax Assets, Valuation Allowance	$ 1,000,000,000				$ 1,000,000,000
Income Taxes Percent Likelihood Of Being Realized Upon Settlement	50.00%				50.00%
Income tax expense	$ (3,000,000)		$ 0		$ (25,000,000)	$ (10,000,000)
Interest and Penalties from Uncertain Tax Positions, Income Tax Benefit					1,000,000
Unrecognized Tax Benefits	$ 30,000,000				30,000,000
Interest and Penalties from Uncertain Tax Positions, Income Tax Expense			$1 million			$1 million
Other Comprehensive Income (Loss) [Member]
Operating Loss Carryforwards [Line Items]
Income tax expense					$ 9,000,000