Retirement Plans (Details 2)	12 Months Ended
May 31, 2011	May 31, 2010	May 31, 2009
Pension Plans
Defined Benefit Plan Assumptions Used In Calculations Abstract
Discount rate used to determine benefit obligation	5.76%	6.37%	7.68%
Discount rate used to determine net periodic benefit cost	6.37%	7.68%	7.15%
Rate of increase in future compensation levels used to determine benefit obligation	4.58%	4.63%	4.42%
Rate of increase in future compensation levels used to determine net periodic benefit cost	4.63%	4.42%	4.49%
Expected long-term rate of return on assets	8.00%	8.00%	8.50%
Postretirement Healthcare Plans
Defined Benefit Plan Assumptions Used In Calculations Abstract
Discount rate used to determine benefit obligation	5.67%	6.11%	7.27%
Discount rate used to determine net periodic benefit cost	6.11%	7.27%	7.13%

The interest rate used to adjust for the time value of money for the plan.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 132R
-Paragraph 5
-Subparagraph j

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- Definition

Expected rate of compensation increases (for pay-related plans).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 132R
-Paragraph 5
-Subparagraph j

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- Definition

The interest rate used to adjust for the time value of money.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 132R
-Paragraph 5
-Subparagraph j

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- Definition

An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 87
-Paragraph 264

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 132R
-Paragraph 5
-Subparagraph j

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- Definition

Expected rate of compensation increases (for pay-related plans).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 132R
-Paragraph 5
-Subparagraph j

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