Basis of presentation and accounting policies - Fiscal year, Cash, Inventory (Details) $ in Millions	12 Months Ended
	Jan. 29, 2016 USD ($) store state period	Jan. 30, 2015 USD ($) period	Jan. 31, 2014 USD ($) period
Basis of presentation
Fiscal year, number of weeks | period	52	52	52
Number of stores through which entity sells general merchandise on a retail basis | store	12,483
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	$ 59.5	$ 58.5
Minimum threshold of cash balances to be maintained as set by insurance regulators	20.0
Merchandise inventories
Excess of current cost over LIFO cost	92.9	95.1
LIFO provision (benefit)	$ (2.3)	$ 4.2	$ (11.0)