Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax	$ (378)	$ (390)
Currency translation adjustments	24	(73)	$ (23)
Cash flow hedge adjustments	(28)	0	(17)
Postretirement benefits adjustments	16	33	(10)
Net other comprehensive income (loss)	12	(40)	(50)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax	(180)	(204)
Net other comprehensive income (loss)	24	(73)	(23)
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	(17)	11
Net other comprehensive income (loss)	(28)	0	(17)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax	(181)	(197)
Net other comprehensive income (loss)	$ 16	$ 33	$ (10)