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Pensions and Other Postretirement Benefits (Details 2)
12 Months Ended
Apr. 30, 2020
Apr. 30, 2019
Apr. 30, 2018
United States [Member] | Defined Benefit Pension Plans [Member]      
Weighted-average assumptions used in determining net periodic benefit costs:      
Discount rate used to determine benefit obligation 3.99% 4.17% 3.95%
Discount rate used to determine service cost 4.20% 4.29% 4.20%
Discount rate used to determine interest cost 3.61% 3.87% 3.38%
Expected return on plan assets 5.28% 5.66% 6.27%
Rate of compensation increase 3.56% 3.59% 3.78%
United States [Member] | Other Postretirement Benefits Plan [Member]      
Weighted-average assumptions used in determining net periodic benefit costs:      
Discount rate used to determine benefit obligation 3.91% 4.13% 3.86%
Discount rate used to determine service cost 4.07% 4.23% 4.06%
Discount rate used to determine interest cost 3.47% 3.79% 3.24%
Expected return on plan assets 0.00% 0.00% 0.00%
Rate of compensation increase 0.00% 0.00% 0.00%
CANADA | Defined Benefit Pension Plans [Member]      
Weighted-average assumptions used in determining net periodic benefit costs:      
Discount rate used to determine benefit obligation 3.21% 3.57% 3.22%
Discount rate used to determine service cost 3.29% 3.64% 3.39%
Discount rate used to determine interest cost 2.86% 3.23% 2.60%
Expected return on plan assets 5.00% 5.25% 5.00%
Rate of compensation increase 3.00% 3.00% 3.00%
CANADA | Other Postretirement Benefits Plan [Member]      
Weighted-average assumptions used in determining net periodic benefit costs:      
Discount rate used to determine benefit obligation 3.19% 3.55% 3.19%
Discount rate used to determine service cost 3.44% 3.77% 3.70%
Discount rate used to determine interest cost 2.86% 3.23% 2.58%
Expected return on plan assets 0.00% 0.00% 0.00%
Rate of compensation increase 0.00% 0.00% 0.00%