Income Taxes - Provision for income taxes (Details) - USD ($) $ in Millions	3 Months Ended									12 Months Ended
	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2016	[1]	Apr. 30, 2016	Jan. 31, 2016	Oct. 31, 2015	Jul. 31, 2015	Apr. 30, 2015	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Federal:
Current										$ 1.6	$ (4.7)	$ (43.8)
Deferred										8.4	220.9	(11.9)
State:
Current										(1.9)	0.5	(13.2)
Deferred										1.3	20.9	9.0
Foreign:
Current										93.9	68.4	69.5
Deferred										(45.0)	4.2	(8.4)
Income tax expense	$ 5.2	$ 13.5	$ 25.2		$ 14.4	$ 16.7	$ 21.3	$ 269.5	$ 2.7	$ 58.3	$ 310.2	$ 1.2

[1] Certain first quarter fiscal 2017 balances have been revised to reflect the adoption of ASU 2016-09. As the adoption occurred in the second quarter of fiscal 2017, we are required to reflect any adjustments as of February 1, 2016, the beginning of the annual period that includes the interim period of adoption, and are required to revise our reported quarterly results for the first quarter. The revision resulted in a $5.3 million decrease of stock-based compensation expense from the previously reported expense. See Note 1, "Business and Summary of Significant Accounting Policies" for further discussion on the adoption.