Goodwill and intangibles - Composition of Finite-Lived Intangibles (Details) - USD ($) $ in Millions	Oct. 31, 2015	Jan. 31, 2015	Nov. 01, 2014
Definite-lived intangible assets:
Gross carrying amount	$ 49.1	$ 49.6	$ 51.3
Accumulated amortization	(19.6)	(9.3)	(6.0)
Net carrying amount	29.5	40.3	45.3
Intangible assets, gross	453.9	456.4	467.3
Total intangible assets, net	434.3	447.1	461.3
Definite-lived intangible liabilities:
Gross carrying amount	(113.9)	(114.3)	(115.6)
Accumulated amortization	48.0	23.5	14.7
Total	(65.9)	(90.8)	(100.9)
Unfavorable leases
Definite-lived intangible liabilities:
Gross carrying amount	(48.3)	(48.7)	(50.0)
Accumulated amortization	20.4	9.7	6.1
Total	(27.9)	(39.0)	(43.9)
Unfavorable contracts
Definite-lived intangible liabilities:
Gross carrying amount	(65.6)	(65.6)	(65.6)
Accumulated amortization	27.6	13.8	8.6
Total	(38.0)	(51.8)	(57.0)
Trade names
Definite-lived intangible assets:
Gross carrying amount	1.5	1.5	1.6
Accumulated amortization	(0.4)	(0.2)	(0.1)
Net carrying amount	1.1	1.3	1.5
Favorable leases
Definite-lived intangible assets:
Gross carrying amount	47.6	48.1	49.7
Accumulated amortization	(19.2)	(9.1)	(5.9)
Net carrying amount	28.4	39.0	43.8
Trade names
Definite-lived intangible assets:
Indefinite-lived trade names	$ 404.8	$ 406.8	$ 416.0