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Pensions and Other Postretirement Benefits (Details 2)
12 Months Ended
Apr. 30, 2015
Apr. 30, 2014
Apr. 30, 2013
U. S. Defined Benefit Plans [Member]      
Weighted-average assumptions used in determining net periodic benefit costs:      
Discount rate 4.42% 3.99% 4.70%
Expected return on plan assets 6.72% 6.75% 7.00%
Rate of compensation increase 4.13% 4.13% 4.12%
U. S. Other Postretirement Benefit Plans [Member]      
Weighted-average assumptions used in determining net periodic benefit costs:      
Discount rate 4.27% 3.80% 4.70%
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 4.11% 3.65% 4.20%
Expected return on plan assets 5.64% 5.78% 6.17%
Rate of compensation increase 3.00% 3.00% 4.00%
Canadian Other Postretirement Benefit Plans [Member]      
Weighted-average assumptions used in determining net periodic benefit costs:      
Discount rate 4.10% 3.70% 4.20%
Expected return on plan assets 0.00% 0.00% 0.00%
Rate of compensation increase 0.00% 0.00% 0.00%