Fair Value of Financial Instruments (Details) (USD $) In Millions, unless otherwise specified	Jul. 31, 2013	Apr. 30, 2013	Jul. 31, 2012	Apr. 30, 2012
Assets:
Cash and cash equivalents, Carrying Amount	$ 217	$ 204	$ 361	$ 338
Liabilities:
Short-term borrowings, Carrying Amount	5	3
Current portion of long-term debt, Carrying Amount	1	2
Long-term debt, Carrying Amount	997	997
Carrying Amount [Member]
Assets:
Cash and cash equivalents, Carrying Amount	217	204
Liabilities:
Short-term borrowings, Carrying Amount	5	3
Current portion of long-term debt, Carrying Amount	1	2
Long-term debt, Carrying Amount	997	997
Carrying Amount [Member] | Currency derivatives [Member]
Assets:
Currency derivatives, Carrying Amount	17	5
Liabilities:
Currency derivatives, Carrying Amount	0	4
Fair Value [Member]
Assets:
Cash and cash equivalents, Fair Value	217	204
Liabilities:
Short-term borrowings, Fair Value	5	3
Current portion of long-term debt, Fair Value	1	2
Long-term debt, Fair Value	950	1,011
Fair Value [Member] | Currency derivatives [Member]
Assets:
Currency derivatives, Fair Value	17	5
Liabilities:
Currency derivatives, Fair Value	$ 0	$ 4