Fair value measurements - Outstanding Debt (Details) - USD ($) $ in Millions	Oct. 31, 2015	Jan. 31, 2015	Nov. 01, 2014
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding debt	$ 1,371.4	$ 1,389.7	$ 1,394.9
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding debt	1,371.3	1,406.5	1,407.0
Senior Notes | Level 2 | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding debt	398.6	398.5	398.4
Senior Notes | Level 2 | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding debt	398.5	415.3	410.5
Securitization Facility | Level 2 | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding debt	600.0	600.0	600.0
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	372.5	390.0	395.0
Term Loan | Level 2 | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding debt	372.5	390.0	395.0
Capital Lease Obligations | Level 2 | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding debt	0.3	1.2	1.5
Capital Lease Obligations | Level 2 | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding debt	$ 0.3	$ 1.2	$ 1.5