Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Jan. 31, 2012	Jan. 31, 2011	Jan. 31, 2012	Jan. 31, 2011
Summarized net income for the other items included in the determination of comprehensive income:
Net income	$ 133.1	$ 140.7	$ 408.7	$ 406.1
Other comprehensive income (loss), net of tax:
Postretirement benefits adjustment	3.3	2.6	9.9	8.3
Foreign currency translation adjustment	(10.4)	1.3	(54.0)	7.0
Net gain (loss) on cash flow hedges	4.6	2.2	13.2	(6.6)
Total Other comprehensive income (loss)	(2.5)	6.1	(30.9)	8.7
Comprehensive income	$ 130.6	$ 146.8	$ 377.8	$ 414.8