Stock-Based Compensation (Schedule of Stock Options and SSARs) (Details) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	12 Months Ended
	Apr. 30, 2013
Stock Options and SSARs, Number of Underlying Shares [Roll Forward]
Stock options and SSARs oustanding, Beginning balance (shares)	5,446
Stock options and SSARs outstanding, Granted (shares)	544
Stock options and SSARs outstanding, Exercised (shares)	(1,367)
Stock options and SSARs outstanding, Forfeited or expired (shares)	(36)
Stock options and SSARs oustanding, Ending balance (shares)	4,587
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)	$ 31.97
Stock options and SSARs outstanding, Weighted Average Exercise Price Per Award, Granted (dollars per share)	$ 58.70
Stock options and SSARs outstanding, Weighted Average Exercise Price Per Award, Exercised (dollars per share)	$ 24.56
Stock options and SSARs outstanding, Weighted Average Exercise Price Per Award, Forfeited or expired (dollars per share)	$ 48.84
Stock options and SSARs outstanding, Weighted Average Exercise Price Per Award, Ending balance (dollars per share)	$ 37.22
Stock options and SSARs outstanding, Weighted Average Remaining Contractual Term (years)	5 years 1 month 6 days
Stock options and SSARs outstanding, Aggregate Intrinsic Value	$ 152
Stock options and SSARs Exercisable (shares)	2,831
Stock options and SSARs Exercisable, Weighted Average Exercise Price Per Award (dollars per share)	$ 30.98
Stock options and SSARs Exercisable, Weighted Average Remaining Contractual Term (years)	3 years 7 months 6 days
Stock options and SSARs Exercisable, Aggregate Intrinsic Value	$ 111