Goodwill and Other Intangible Assets (Details) $ in Millions	3 Months Ended
	Jul. 31, 2017 USD ($)
Goodwill [Roll Forward]
Balance at April 30, 2017	$ 753
Foreign currency translation adjustment	2
Balance at July 31, 2017	755
Indefinite-lived Intangible Assets [Roll Forward]
Balance at April 30, 2017	641
Foreign currency translation adjustment	20
Balance at July 31, 2017	$ 661