Stockholders' Equity Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2017	Jan. 31, 2019	Jan. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			$ (378)				$ (378)
Net other comprehensive income (loss)	$ 5	$ (1)	14	$ 9	$ (15)	$ 14	18	$ 8
Ending balance	(360)						(360)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(180)				(180)
Net other comprehensive income (loss)	18			38			(21)	47
Ending balance	(201)						(201)
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)	(8)			(32)			37	(48)
Ending balance	20						20
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)	(5)			$ 3			2	$ 9
Ending balance	$ (179)						$ (179)