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Pensions and Other Postretirement Benefits (Details 6) - Defined Benefit Pension Plans [Member] - USD ($)
$ in Millions
Apr. 30, 2018
Apr. 30, 2017
Additional information related to the Company's defined benefit pension plans    
Accumulated benefit obligation for all pension plans $ 627.9 $ 659.6
Plans with an accumulated benefit obligation in excess of plan assets:    
Accumulated benefit obligation 541.3 570.6
Fair value of plan assets 400.6 394.4
Plans with a projected benefit obligation in excess of plan assets:    
Projected benefit obligation 552.9 588.2
Fair value of plan assets $ 400.6 $ 394.4