Basis of presentation and accounting policies - Fiscal year, Cash, Inventory (Details) $ in Millions	12 Months Ended
	Feb. 03, 2017 USD ($) store state period	Jan. 29, 2016 USD ($) period	Jan. 30, 2015 USD ($) period
Basis of presentation
Fiscal year, number of weeks | period	53	52	52
Number of stores through which entity sells general merchandise on a retail basis | store	13,320
Number of states which entity covers | state	43
Cash and cash equivalents
Maximum original maturity period at time of purchase of liquid investments classified as cash equivalents	3 months
Payments due from processors for electronic tender transactions classified as cash and cash equivalents	$ 73.9	$ 59.5
Minimum threshold of cash balances to be maintained as set by insurance regulators	20.0
Merchandise inventories
Excess of current cost over LIFO cost	80.7	92.9
LIFO provision (benefit)	$ (12.2)	$ (2.3)	$ 4.2