Stock-Based Compensation (Schedule of Stock Options and SSARs) (Details) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Apr. 30, 2017 USD ($) $ / shares shares
Stock Options and SSARs, Number of Underlying Shares [Roll Forward]
Stock options and SSARs oustanding, Beginning balance (shares) | shares	6,852
Stock options and SSARs outstanding, Granted (shares) | shares	779
Stock options and SSARs outstanding, Exercised (shares) | shares	(1,005)
Stock options and SSARs outstanding, Forfeited or expired (shares) | shares	(11)
Stock options and SSARs oustanding, Ending balance (shares) | shares	6,615
Stock Options and SSARs, Weighted Average Exercise Price [Roll Forward]
Stock options and SSARs outstanding, Weighted Average Exercise Price Per Award, Beginning balance (dollars per share) | $ / shares	$ 28.42
Stock options and SSARs outstanding, Weighted Average Exercise Price Per Award, Granted (dollars per share) | $ / shares	49.01
Stock options and SSARs outstanding, Weighted Average Exercise Price Per Award, Exercised (dollars per share) | $ / shares	19.49
Stock options and SSARs outstanding, Weighted Average Exercise Price Per Award, Forfeited or expired (dollars per share) | $ / shares	46.79
Stock options and SSARs outstanding, Weighted Average Exercise Price Per Award, Ending balance (dollars per share) | $ / shares	$ 32.17
Stock options and SSARs outstanding, Weighted Average Remaining Contractual Term (years)	4 years 11 months 26 days
Stock options and SSARs outstanding, Aggregate Intrinsic Value | $	$ 104
Stock options and SSARs Exercisable (shares) | shares	4,390
Stock options and SSARs Exercisable, Weighted Average Exercise Price Per Award (dollars per share) | $ / shares	$ 23.75
Stock options and SSARs Exercisable, Weighted Average Remaining Contractual Term (years)	3 years 6 months 29 days
Stock options and SSARs Exercisable, Aggregate Intrinsic Value | $	$ 103