Stockholders' Equity Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Oct. 31, 2018	Jul. 31, 2018	Oct. 31, 2017	Jul. 31, 2017	Oct. 31, 2018	Oct. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		$ (378)			$ (378)
Net other comprehensive income (loss)	$ (1)	14	$ (15)	$ 14	13	$ (1)
Ending balance	(365)				(365)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(180)			(180)
Net other comprehensive income (loss)	(27)		(25)		(39)	9
Ending balance	(219)				(219)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(17)			(17)
Net other comprehensive income (loss)	22		7		45	(16)
Ending balance	28				28
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		$ (181)			(181)
Net other comprehensive income (loss)	4		$ 3		7	$ 6
Ending balance	$ (174)				$ (174)