Risk Management Activities (Narrative) (Details) $ in Millions	3 Months Ended	9 Months Ended
	Feb. 28, 2016 USD ($)	Feb. 28, 2016 USD ($)
Credit Risk [Abstract]
Accounts Payable to Suppliers that Utilize Third Party Service	$ 508.0	$ 508.0
Commodity Contracts [Member]
Derivative [Line Items]
Derivative, Notional Amount	343.4	$ 343.4
Derivative Contracts Inputs, Average Period of Utilization		12 months
Energy Related Derivative [Member]
Derivative [Line Items]
Derivative, Notional Amount	146.9	$ 146.9
Agricultural Related Derivative [Member]
Derivative [Line Items]
Derivative, Notional Amount	196.5	196.5
Treasury Lock [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 400.0	$ 400.0
Derivative, Average Fixed Interest Rate	2.10%	2.10%
Derivative, Maturity Date	Feb. 15, 2017