Pensions and Other Postretirement Benefits (Details 2)	12 Months Ended
Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
U. S. Defined Benefit Plans [Member]
Weighted-average assumptions used in determining net periodic benefit costs:
Discount rate	3.85%	4.06%	4.42%
Expected return on plan assets	6.27%	6.58%	6.72%
Rate of compensation increase	3.96%	4.06%	4.13%
U. S. Other Postretirement Benefit Plans [Member]
Weighted-average assumptions used in determining net periodic benefit costs:
Discount rate	3.80%	4.04%	4.27%
Expected return on plan assets	0.00%	0.00%	0.00%
Rate of compensation increase	0.00%	0.00%	0.00%
Canadian Defined Benefit Plans [Member]
Weighted-average assumptions used in determining net periodic benefit costs:
Discount rate	3.60%	3.51%	4.11%
Expected return on plan assets	5.25%	5.65%	5.64%
Rate of compensation increase	3.00%	3.00%	3.00%
Canadian Other Postretirement Benefit Plans [Member]
Weighted-average assumptions used in determining net periodic benefit costs:
Discount rate	3.50%	3.50%	4.10%
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 Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(1)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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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 Accounting Standards Codification
-Glossary Expected Long-Term Rate of Return on Plan Assets
-URI http://asc.fasb.org/extlink&oid=6512046

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(3)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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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 Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(2)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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- References

No definition available.

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