Common Shares (Details) shares in Millions	12 Months Ended
	Apr. 30, 2020 votes_per_share shares	Apr. 30, 2019 shares
Stockholders' Equity Note [Abstract]
Number of votes each holder of a common share outstanding is entitled	1
Number of votes per share	10
Number of years required to pass after change in beneficial ownership	4 years
Number of votes per share after change in beneficial ownership	1
Shares repurchased during period, shares | shares	0.0	0.0
Shares remaining for repurchase | shares	3.6