Pension and Other Postretirement Benefits (Assumptions and SensItivity) (Details)	12 Months Ended
Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Pension Benefits [Member]
Assumptions used in computing benefit plan obligations
Discount rate (percent)	4.23%	4.09%
Rate of salary increase (percent)	4.00%	4.00%
Assumptions used in computing benefit plan expense
Discount rate for service cost (percent)	4.29%	4.02%	4.09%
Discount rate for interest cost (percent)	3.40%	4.02%	4.09%
Rate of salary increase (percent)	4.00%	4.00%	4.00%
Expected return on plan assets (percent)	6.75%	7.00%	7.00%
Medical and Life Insurance Benefits [Member]
Assumptions used in computing benefit plan obligations
Discount rate (percent)	4.20%	4.04%
Assumptions used in computing benefit plan expense
Discount rate for service cost (percent)	4.39%	3.96%	4.09%
Discount rate for interest cost (percent)	3.35%	3.96%	4.09%
Assumed health care cost trend rates
Present rate (percent)	7.70%	7.25%
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	5.00%	5.00%

Defined Benefit Plan, Assumption Used Calculating Net Periodic Benefit Cost, Discount Rate, Interest Cost

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- Definition

Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate, Service Cost

+ References

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- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

+ 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)(1)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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- Definition

Weighted average rate increase of compensation, used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

+ 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=82843861&loc=d3e1928-114920

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- Definition

Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan.

+ 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)(3)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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- Definition

Weighted average rate of compensation increase used to determine net periodic benefit cost of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

+ 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=82843861&loc=d3e1928-114920

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- Definition

Assumed rate, for next fiscal year, based on annual change in cost of health care cost benefits used to measure expected cost of benefits covered by defined benefit postretirement plan. Factors include, but are not limited to, estimate of health care inflation, change in health care utilization or delivery pattern, technological advances, and change in health status of participant. Excludes factors for change in composition of plan population by age and dependency status.

+ 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 (l)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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- Definition

Ultimate trend rate for health care cost for defined benefit postretirement plan.

+ 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 (l)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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