Employee Benefit Plans (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	May 31, 2014	May 31, 2013	May 31, 2012	May 31, 2011
Employee Benefit Plans (Details) [Line Items]
Defined Benefit Post Retirement Plan Unrecognized Prior Service Credit		$ 0.5
Percentage Of Federal Subsidy To Sponsors Of Retiree Health Care Benefit Plans		28.00%
Prescription Drug Benefit, Reduction in Accumulated Postretirement Benefit Obligation for Subsidy		3.1	2.9	3.0
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets		7.30%
Other Comprehensive Income Defined Benefit Plans Tax (Expense) Benefit		8.4	(6.5)
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year	8.3
Defined Retirement Plan Contributed		8.0	7.4	6.9
Estimated Net Loss [Member] | Pension Plan, Defined Benefit [Member]
Employee Benefit Plans (Details) [Line Items]
Defined Benefit Plan, Amount to be Amortized from Accumulated Other Comprehensive Income (Loss) Next Fiscal Year	1.8
Estimated Net Loss [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Employee Benefit Plans (Details) [Line Items]
Defined Benefit Plan, Amount to be Amortized from Accumulated Other Comprehensive Income (Loss) Next Fiscal Year	2.5
Prior Service Credit [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Employee Benefit Plans (Details) [Line Items]
Defined Benefit Plan, Amount to be Amortized from Accumulated Other Comprehensive Income (Loss) Next Fiscal Year	0.2
Pension Plan, Defined Benefit [Member]
Employee Benefit Plans (Details) [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets		7.30%	7.70%	7.50%
Annuities [Member]
Employee Benefit Plans (Details) [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		$ 6.1	$ 5.8