Pensions and Other Postretirement Benefits (Details 4) - USD ($) $ in Millions	12 Months Ended
Apr. 30, 2017	Apr. 30, 2016
Defined Benefit Pension Plans [Member]
Accumulated other comprehensive income (loss)
Net actuarial (loss) gain	$ (166.4)	$ (212.3)
Prior service (cost) credit	(5.6)	(8.8)
Total recognized in accumulated other comprehensive loss	(172.0)	(221.1)
Other Postretirement Benefits [Member]
Accumulated other comprehensive income (loss)
Net actuarial (loss) gain	8.5	6.3
Prior service (cost) credit	10.7	9.2
Total recognized in accumulated other comprehensive loss	19.2	$ 15.5
One-percentage point annual change in the assumed health care cost trend rate
Effect on total service and interest cost components, increase	0.1
Effect on total service and interest cost components, decrease	0.1
Effect on benefit obligation, increase	1.4
Effect on benefit obligation, decrease	$ 1.4
U. S. Defined Benefit Plans [Member]
Weighted-average assumptions used in determining benefit obligation
Discount rate	3.95%	3.76%
Rate of compensation increase	4.15%	3.96%
U. S. Other Postretirement Benefit Plans [Member]
Weighted-average assumptions used in determining benefit obligation
Discount rate	3.86%	3.80%
Rate of compensation increase	0.00%	0.00%
Canadian Defined Benefit Plans [Member]
Weighted-average assumptions used in determining benefit obligation
Discount rate	3.22%	3.60%
Rate of compensation increase	3.00%	3.00%
Canadian Other Postretirement Benefit Plans [Member]
Weighted-average assumptions used in determining benefit obligation
Discount rate	3.16%	3.50%
Rate of compensation increase	0.00%	0.00%

The pretax total of net gain (loss), prior service cost (credit), and transition assets (obligations), as well as minimum pension liability if still remaining, included in accumulated other comprehensive income associated with a defined benefit pension or other postretirement plan(s) because they have yet to be recognized as components of net periodic benefit cost.

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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (i-k)
-URI http://asc.fasb.org/extlink&oid=66004124&loc=SL7669646-108580

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The pretax net amount of gains and losses that are not yet recognized as a component of net periodic benefit cost, and that are recognized as increases or decreases in other comprehensive income as they arise. Gains and losses are due to changes in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=66004124&loc=SL7669646-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Section 50
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-Subparagraph (j)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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- Definition

Amount related to the pretax cost of benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation, which has not yet been recognized as components of net periodic benefit cost.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Prior Service Cost
-URI http://asc.fasb.org/extlink&oid=49177896

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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
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- Definition

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

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- Definition

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

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Amount of effect of a one-percentage-point decrease in the assumed health care cost trend rates on the accumulated postretirement benefit obligation for health care benefits.

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Amount of effect of a one-percentage-point decrease in the assumed health care cost trend rates on the aggregate of the service and interest cost components of net periodic postretirement health care benefit costs.

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The effect of a one-percentage-point increase in the assumed health care cost trend rates on the accumulated postretirement benefit obligation for health care benefits.

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The effect of a one-percentage-point increase in the assumed health care cost trend rates on the aggregate of the service and interest cost components of net periodic postretirement health care benefit costs.

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