Stockholders' Equity Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Jan. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			$ (390)
Net other comprehensive income (loss)	$ 9	$ (26)	8	$ (83)
Ending balance	(382)		(382)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(204)
Net other comprehensive income (loss)	38	(25)	47	(110)
Ending balance	(157)		(157)
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)	(32)	(7)	(48)	14
Ending balance	(37)		(37)
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	$ 6	9	$ 13
Ending balance	$ (188)		$ (188)