Goodwill and Other Intangible Assets (Details) $ in Millions	9 Months Ended
	Jan. 31, 2018 USD ($)
Goodwill [Roll Forward]
Balance at April 30, 2017	$ 753
Foreign currency translation adjustment	15
Balance at January 31, 2018	768
Indefinite-lived Intangible Assets [Roll Forward]
Balance at April 30, 2017	641
Foreign currency translation adjustment	39
Balance at January 31, 2018	$ 680