Goodwill and Other Intangible Assets (Details) $ in Millions	6 Months Ended
	Oct. 31, 2017 USD ($)
Goodwill [Roll Forward]
Balance at April 30, 2017	$ 753
Foreign currency translation adjustment	3
Balance at October 31, 2017	756
Indefinite-lived Intangible Assets [Roll Forward]
Balance at April 30, 2017	641
Foreign currency translation adjustment	18
Balance at October 31, 2017	$ 659