Inventories - Rollforward of Inventory Reserves (Details) - USD ($) $ in Millions	12 Months Ended
	Jan. 28, 2017	Jan. 30, 2016	Jan. 31, 2015
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	$ 43.2	$ 28.4	$ 16.3
Charged to profit	57.3	87.6	44.6
Utilized	(57.3)	(72.8)	(32.5)
Balance at end of period	$ 43.2	$ 43.2	$ 28.4