Accounts receivable, net - Credit Quality Indicator and Age Analysis (Details) (USD $) In Millions, unless otherwise specified	May 02, 2015	Jan. 31, 2015	May 03, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross	$ 1,592.7	$ 1,666.0	$ 1,382.6
Valuation allowance	(103.3)	(113.1)	(87.8)
Gross	100.00%	100.00%	100.00%
Valuation allowance	6.50%	6.80%	6.40%
Performing Financing Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross	96.50%	96.20%	96.70%
Valuation allowance	3.10%	3.10%	3.10%
Performing Financing Receivable | Period One | 0 to 30 Days Aged Performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross	1,290.9	1,332.2	1,130.8
Valuation allowance	(39.3)	(41.1)	(34.4)
Performing Financing Receivable | Period Two | 31 to 90 Days Aged Performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross	246.4	271.1	205.6
Valuation allowance	(8.6)	(9.3)	(7.2)
Nonperforming Financing Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross	3.50%	3.80%	3.30%
Valuation allowance	100.00%	100.00%	100.00%
Nonperforming Financing Receivable | Period Two | More Than 90 Days Aged Non Performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross	55.4	62.7	46.2
Valuation allowance	$ (55.4)	$ (62.7)	$ (46.2)