Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended		12 Months Ended
	Oct. 31, 2015	Oct. 31, 2016	Oct. 31, 2015	Jan. 31, 2017
Income taxes
Net unrecognized tax benefits that would affect effective tax rate, if recognized	$ 10.3	$ 12.3	$ 10.3
Liability for unrecognized tax benefits for interest and penalties	1.1	1.7	1.1
Income tax expense (benefit)	$ (237.5)	$ 10.3	$ (221.7)
Forecast
Income taxes
Effective tax rate (as a percent)				27.50%