Income Taxes (Components of Income Tax Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Apr. 30, 2016	Apr. 30, 2015	Apr. 30, 2014
Current:
U.S. federal	$ 347	$ 259	$ 243
Foreign	47	42	49
State and local	18	11	1
Current income tax expense	412	312	293
Deferred:
U.S. federal	24	15	3
Foreign	(17)	(11)	(6)
State and local	3	2	(2)
Deferred income taxes expense	10	6	(5)
Total income tax expense	$ 422	$ 318	$ 288