Fair value measurements - Outstanding Debt (Details) - USD ($) $ in Millions	Apr. 29, 2017	Jan. 28, 2017	Apr. 30, 2016
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding debt	$ 1,334.4	$ 1,338.5	$ 1,347.1
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding debt	1,340.6	1,339.8	1,352.7
Senior Notes | Level 2 | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding debt	393.9	393.7	393.0
Senior Notes | Level 2 | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding debt	396.5	391.2	395.1
Securitization Facility | Level 2 | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding debt	599.7	599.7	599.9
Securitization Facility | Level 2 | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding debt	600.0	600.0	600.0
Term Loan | Level 2 | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding debt	340.8	345.1	354.1
Term Loan | Level 2 | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding debt	344.1	348.6	357.5
Capital Lease Obligations | Level 2 | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding debt	0.0	0.0	0.1
Capital Lease Obligations | Level 2 | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding debt	$ 0.0	$ 0.0	$ 0.1