Income Taxes (Components of Income Tax Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Current:
U.S. federal	$ 265	$ 226	$ 347
Foreign	47	40	47
State and local	17	8	18
Current income tax expense	329	274	412
Deferred:
U.S. federal	(48)	(1)	24
Foreign	(13)	(9)	(17)
State and local	(8)	0	3
Deferred income taxes expense	(69)	(10)	10
Total income tax expense	$ 260	$ 264	$ 422