Debt and Credit Facilities Short-term borrowings (Details) - USD ($) $ in Millions	12 Months Ended
	Apr. 30, 2016	Apr. 30, 2015
Short-term Debt [Abstract]
Short-term borrowings	$ 271	$ 190
Commercial Paper	$ 269	$ 183
Commercial Paper Borrowings, Weighted Average Interest Rate	0.53%	0.17%
Commercial Paper Borrowings, Average Remaining Maturity	26 days	13 days