Net Loss Per Share (Computation of Basic and Diluted Net Loss Per Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Oct. 31, 2020	Oct. 31, 2019
Earnings Per Share [Abstract]
Net loss	$ (92.2)	$ (59.6)
Weighted-average shares used to compute net loss per share, basic and diluted	95.5	96.6
Net loss per share, basic and diluted (in usd per share)	$ (0.97)	$ (0.62)