Debt Short-term borrowings (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Jan. 31, 2016	Apr. 30, 2015
Short-term Debt [Abstract]
Short-term borrowings	$ 509	$ 190
Commercial Paper	$ 506	$ 183
Commercial Paper Borrowings, Weighted Average Interest Rate	0.61%	0.17%
Commercial Paper Borrowings, Average Remaining Maturity	37 days	13 days