Debt and Financing Arrangements (Details) (USD $) In Millions, unless otherwise specified	Oct. 31, 2014	Apr. 30, 2014
Debt and Financing Arrangements [Abstract]
Total long-term debt	$ 1,890.8	$ 1,979.8
Current portion of long-term debt	0	100.0
Total long-term debt, less current portion	1,890.8	1,879.8
4.78% Senior Notes due June 1, 2014 [Member]
Debt Instrument [Line Items]
Company issued Senior Notes	0	100.0
Percentage of notes	4.78%	4.78%
6.12% Senior Notes due November 1, 2015 [Member]
Debt Instrument [Line Items]
Company issued Senior Notes	24.0	24.0
Percentage of notes	6.12%	6.12%
6.63% Senior Notes due November 1, 2018 [Member]
Debt Instrument [Line Items]
Company issued Senior Notes	390.4	392.0
Percentage of notes	6.63%	6.63%
3.50% Senior Notes due October 15, 2021 [Member]
Debt Instrument [Line Items]
Company issued Senior Notes	776.4	763.8
Percentage of notes	3.50%	3.50%
5.55% Senior Notes due April 1, 2022 [Member]
Debt Instrument [Line Items]
Company issued Senior Notes	300.0	300.0
Percentage of notes	5.55%	5.55%
4.50% Senior Notes due June 1, 2025 [Member]
Debt Instrument [Line Items]
Company issued Senior Notes	$ 400.0	$ 400.0
Percentage of notes	4.50%	4.50%