Income Taxes (Components of Income Tax Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Apr. 30, 2019	Apr. 30, 2018	Apr. 30, 2017
Current:
U.S. federal	$ 107	$ 265	$ 226
Foreign	34	47	40
State and local	28	17	8
Current income tax expense	169	329	274
Deferred:
U.S. federal	37	(48)	(1)
Foreign	4	(13)	(9)
State and local	(3)	(8)	0
Deferred income taxes expense	38	(69)	(10)
Total income tax expense	$ 207	$ 260	$ 264