Stock-Based Compensation (Textual) (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Apr. 30, 2014	Apr. 30, 2013	Apr. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
The total intrinsic value of options and SSARs exercised	$ 48	$ 52	$ 29
Stock options and SSARs award vesting period (years)	3 years
Stock options and SSARs award expiration period (years)	7 years
Grant-date fair value per award (dollars per share)	$ 14.84	$ 10.70	$ 9.40
Stock-based incentive awards on a pre-tax	13	11	9
Compensation expense partially offset by deferred income tax benefits	5	4	4
Total unrecognized compensation cost related to non-vested stock-based compensation	14
Unrecognized compensation cost, weighted-average period of recognition (years)	2 years 7 months 6 days
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding under Restricted stock units (shares)	365,000
Weighted-average remaining restriction period (years)	2 years
Total fair value of RSUs, restricted stock, and DSUs vested	$ 11	$ 5	$ 2
Omnibus Compensation Plan 2004 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized under 2013 Omnibus Compensation Plan (shares)	8,300,000
Shares issued under 2013 Omnibus Compensation Plan (shares)	7,760,000