Income Taxes (Components of Income Tax Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Current:
U.S. federal	$ 226	$ 347	$ 259
Foreign	40	47	42
State and local	8	18	11
Current income tax expense	274	412	312
Deferred:
U.S. federal	(1)	24	15
Foreign	(9)	(17)	(11)
State and local	0	3	2
Deferred income taxes expense	(10)	10	6
Total income tax expense	$ 264	$ 422	$ 318