Pension and Other Postretirement Benefits (Schedule of Components of Pension Expense) (Details) - Pension Benefits [Member] - USD ($) $ in Millions	12 Months Ended
	Apr. 30, 2016	Apr. 30, 2015	Apr. 30, 2014
Pension Expense
Service cost	$ 26	$ 22	$ 21
Interest cost	35	34	31
Expected return on assets	(40)	(41)	(40)
Amortization of prior service cost (credit)	1	1	1
Amortization of net actuarial loss (gain)	27	22	31
Net expense	$ 49	$ 38	$ 44