Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended				6 Months Ended
	Oct. 31, 2022	Jul. 31, 2022	Oct. 31, 2021	Jul. 31, 2021	Oct. 31, 2022	Oct. 31, 2021
Schedule of Earnings Per Share, Two Class Method [Line Items]
Net income	$ 191.1	$ 109.8	$ 206.0	$ 153.9	$ 300.9	$ 359.9
Weighted-average common shares outstanding (in shares)	106.5				106.4
Weighted-average common shares outstanding – assuming dilution (in shares)	106.9				106.8
Net income per common share (in dollars per share)	$ 1.79		$ 1.90		$ 2.82	$ 3.32
Net Income - Assuming Dilution (in dollars per share)	$ 1.79		$ 1.90		$ 2.82	$ 3.32
Two-class method
Schedule of Earnings Per Share, Two Class Method [Line Items]
Net income	$ 191.1		$ 206.0		$ 300.9	$ 359.9
Less: Net income allocated to participating securities	0.3		0.6		0.5	1.1
Net income allocated to common stockholders	$ 190.8		$ 205.4		$ 300.4	$ 358.8
Weighted-average common shares outstanding (in shares)	106.5		108.1		106.4	108.0
Add: Dilutive effect of stock options (in shares)	0.0		0.0		0.1	0.1
Weighted-average common shares outstanding – assuming dilution (in shares)	106.5		108.1		106.5	108.1
Net income per common share (in dollars per share)	$ 1.79		$ 1.90		$ 2.82	$ 3.32
Net Income - Assuming Dilution (in dollars per share)	$ 1.79		$ 1.90		$ 2.82	$ 3.32