Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax	$ (390)	$ (350)
Currency translation adjustments	(73)	(23)	$ (114)
Cash flow hedge adjustments	0	(17)	32
Postretirement benefits adjustments	33	(10)	(30)
Net other comprehensive income (loss)	(40)	(50)	(112)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax	(204)	(131)
Net other comprehensive income (loss)	(73)	(23)	(114)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax	11	11
Net other comprehensive income (loss)	0	(17)	32
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax	(197)	(230)
Net other comprehensive income (loss)	$ 33	$ (10)	$ (30)