Fair Value of Financial Instruments (Details) (USD $) In Millions, unless otherwise specified	Jul. 31, 2012	Apr. 30, 2012	Jul. 31, 2011	Apr. 30, 2011
Assets:
Cash and cash equivalents, Carrying Amount	$ 361.5	$ 338.3	$ 552.5	$ 567.1
Cash and cash equivalents, Fair Value	361.5
Liabilities:
Short-term borrowings, Carrying Amount	6.5	4.3
Short-term borrowings, Fair Value	6.5
Current portion of long-term debt, Carrying Amount	2.7	2.7
Current portion of long-term debt, Fair Value	2.7
Long-term debt, Carrying Amount	502.1	502.8
Long -term debt, Fair Value	529.6
Currency derivatives [Member]
Assets:
Contracts, Carrying Amount	8.0
Contracts, fair value	8.0
Liabilities:
Currency derivatives, Carrying Amount	4.7
Currency derivatives, Fair Value	4.7
Interest rate swaps [Member]
Assets:
Contracts, Carrying Amount	2.2
Contracts, fair value	$ 2.2