Stockholders' Equity Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			$ (390)
Net other comprehensive income (loss)	$ (15)	$ (5)	(1)	$ (57)
Ending balance	(391)		(391)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(204)
Net other comprehensive income (loss)	(25)	(18)	9	(85)
Ending balance	(195)		(195)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			11
Net other comprehensive income (loss)	7	9	(16)	21
Ending balance	(5)		(5)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(197)
Net other comprehensive income (loss)	3	$ 4	6	$ 7
Ending balance	$ (191)		$ (191)