Employee and Retiree Benefits (Narrative) (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended			9 Months Ended
	Jan. 31, 2014	Jan. 31, 2013	Jan. 31, 2012	May 31, 2014
Compensation and Retirement Disclosure [Abstract]
Postretirement health care benefits age requirement before distribution occurs				55 years
Postretirement health care benefits continuous service requirement				15 years
Dollar cap liability reduction	10.00%	10.00%	10.00%
Plan amendment liability reduction	$ (3.6)	$ (4.3)	$ (4.6)
Plan amendment amortization period	7 years 4 months 0 days	7 years 6 months 0 days	7 years 9 months 20 days