Fair Value of Financial Instruments (Details) (USD $) In Millions, unless otherwise specified	Jan. 31, 2013	Apr. 30, 2012	Jan. 31, 2012	Apr. 30, 2011
Assets:
Cash and cash equivalents, Carrying Amount	$ 386.8	$ 338.3	$ 494.9	$ 567.1
Cash and cash equivalents, Fair Value	386.8
Liabilities:
Short-term borrowings, Carrying Amount	10.6	4.3
Short-term borrowings, Fair Value	10.6
Current portion of long-term debt, Carrying Amount	253.7	2.7
Current portion of long-term debt, Fair Value	261.6
Long-term debt, Carrying Amount	996.6	502.8
Long-term debt, Fair Value	994.0
Currency derivatives [Member]
Assets:
Contracts, Carrying Amount	1.9
Contracts, Fair Value	1.9
Liabilities:
Currency derivatives, Carrying Amount	13.3
Currency derivatives, Fair Value	13.3
Interest rate swaps [Member]
Assets:
Contracts, Carrying Amount	1.8
Contracts, Fair Value	$ 1.8