Income Taxes - Narrative (Details) - USD ($)	1 Months Ended		3 Months Ended				6 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Apr. 30, 2019	Jan. 31, 2019	Apr. 30, 2018	Jan. 31, 2017	Apr. 30, 2019	Apr. 30, 2018
Operating Loss Carryforwards [Line Items]
Unusual or Infrequent Item, or Both, Tax Effect	$ 38,000,000
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
Effective Income Tax Rate Reconciliation, Repatriation of Foreign Earnings, Amount		$ 147,000,000
Income Taxes Percent Likelihood Of Being Realized Upon Settlement			50.00%				50.00%
Income Tax Expense (Benefit)			$ (1,000,000)	$ (1,000,000)	$ 7,000,000		$ (20,000,000)	$ 22,000,000
Unrecognized Tax Benefits			$ 21,000,000				$ 21,000,000
Interest and Penalties from Uncertain Tax Positions, Income Tax Expense							1
Other Comprehensive Income (Loss) [Member]
Operating Loss Carryforwards [Line Items]
Income Tax Expense (Benefit)							$ (9,000,000)