Stock-Based Compensation (Schedule of Stock Options and SSARs) (Details) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Apr. 30, 2018 USD ($) $ / shares shares
Stock Options and SSARs, Number of Underlying Shares [Roll Forward]
Stock options and SSARs oustanding, Beginning balance (shares) | shares	8,278
Stock options and SSARs outstanding, Granted (shares) | shares	1,059
Stock options and SSARs outstanding, Exercised (shares) | shares	(2,116)
Stock options and SSARs outstanding, Forfeited or expired (shares) | shares	(6)
Stock options and SSARs oustanding, Ending balance (shares) | shares	7,215
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	$ 25.74
Stock options and SSARs outstanding, Weighted Average Exercise Price Per Award, Granted (dollars per share) | $ / shares	39.07
Stock options and SSARs outstanding, Weighted Average Exercise Price Per Award, Exercised (dollars per share) | $ / shares	17.11
Stock options and SSARs outstanding, Weighted Average Exercise Price Per Award, Forfeited or expired (dollars per share) | $ / shares	36.05
Stock options and SSARs outstanding, Weighted Average Exercise Price Per Award, Ending balance (dollars per share) | $ / shares	$ 29.67
Stock options and SSARs outstanding, Weighted Average Remaining Contractual Term (years)	5 years 4 months 24 days
Stock options and SSARs outstanding, Aggregate Intrinsic Value | $	$ 190
Stock options and SSARs Exercisable (shares) | shares	4,335
Stock options and SSARs Exercisable, Weighted Average Exercise Price Per Award (dollars per share) | $ / shares	$ 23.17
Stock options and SSARs Exercisable, Weighted Average Remaining Contractual Term (years)	3 years 8 months 19 days
Stock options and SSARs Exercisable, Aggregate Intrinsic Value | $	$ 142