Income taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jul. 29, 2011	Jul. 30, 2010	Jul. 29, 2011	Jul. 30, 2010
Income taxes
Percentage of likelihood of realization that the tax position must exceed in order for the amount to be recognized (as a percent)			50.00%
Reserves for uncertain tax benefits	$ 26.5		$ 26.5
Interest accrued related to uncertain tax benefits	2.4		2.4
Penalties accrued related to uncertain tax benefits	0.5		0.5
Aggregate reserve for uncertain tax positions including interest and penalties	29.4		29.4
Reserves for uncertain tax benefits included in current liabilities as accrued expenses and other	0.2		0.2
Reserves for uncertain tax benefits included in noncurrent other liabilities	27.9		27.9
Deferred tax assets related to net operating loss carry forwards	1.3		1.3
Expected reduction in reserve for uncertain tax position in next twelve months	1.4		1.4
Expected reduction in reserve for uncertain tax position in next twelve months included in accrued expenses and other	0.2		0.2
Expected reduction in reserve for uncertain tax position in next twelve months included in noncurrent other liabilities	1.2		1.2
Reserve for uncertain tax positions that would impact effective tax rate if recognized	$ 26.5		$ 26.5
Effective income tax rate (as a percent)	36.80%	37.20%	37.50%	37.50%
Decrease in the effective income tax rate during the period (as a percent)	0.40%