Pensions and Other Postretirement Benefits (Details 2)	12 Months Ended
Apr. 30, 2011	Apr. 30, 2010	Apr. 30, 2009
Defined Benefit Pension Plans [Member] \| U.S. plans [Member]
Weighted-average assumptions used
Discount rate	5.80%	7.40%	6.60%
Expected return on plan assets	7.50%	7.75%	7.75%
Rate of compensation increase	4.15%	3.79%	3.84%
Defined Benefit Pension Plans [Member] \| Canadian plans [Member]
Weighted-average assumptions used
Discount rate	5.30%	5.40%	6.10%
Expected return on plan assets	7.08%	7.33%	7.25%
Rate of compensation increase	4.00%	4.00%	4.00%
Other Postretirement Benefits [Member] \| U.S. plans [Member]
Weighted-average assumptions used
Discount rate	5.80%	7.40%	6.60%
Expected return on plan assets	0.00%	0.00%	0.00%
Rate of compensation increase	0.00%	0.00%	0.00%
Other Postretirement Benefits [Member] \| Canadian plans [Member]
Weighted-average assumptions used
Discount rate	5.30%	5.40%	6.10%
Expected return on plan assets	0.00%	0.00%	0.00%
Rate of compensation increase	0.00%	0.00%	0.00%

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

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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