Condensed Consolidated Statements of Comprehensive Income (Unaudited) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Jan. 31, 2013	Jan. 31, 2012	Jan. 31, 2013	Jan. 31, 2012
Statement of Other Comprehensive Income [Abstract]
Net income	$ 157.6	$ 133.1	$ 478.0	$ 408.7
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustment	14.0	(10.4)	13.2	(54.0)
Postretirement benefits adjustment	4.5	3.3	13.8	9.9
Net gain (loss) on cash flow hedges	(1.9)	4.6	(3.2)	13.2
Net other comprehensive (loss) income	16.6	(2.5)	23.8	(30.9)
Comprehensive income	$ 174.2	$ 130.6	$ 501.8	$ 377.8