Goodwill and intangibles - Composition of Finite-Lived Intangibles (Details) - USD ($) $ in Millions	Aug. 01, 2015	Jan. 31, 2015	Aug. 02, 2014
Definite-lived intangible assets:
Gross carrying amount	$ 49.1	$ 49.6	$ 51.8
Accumulated amortization	(16.1)	(9.3)	(2.4)
Net carrying amount	33.0	40.3	49.4
Intangible assets, gross	453.9	456.4	470.0
Total intangible assets, net	437.8	447.1	467.6
Definite-lived intangible liabilities:
Gross carrying amount	(113.9)	(114.3)	(116.1)
Accumulated amortization	41.0	23.5	5.9
Total	(72.9)	(90.8)	(110.2)
Unfavorable leases
Definite-lived intangible liabilities:
Gross carrying amount	(48.3)	(48.7)	(50.5)
Accumulated amortization	16.8	9.7	2.4
Total	(31.5)	(39.0)	(48.1)
Unfavorable contracts
Definite-lived intangible liabilities:
Gross carrying amount	(65.6)	(65.6)	(65.6)
Accumulated amortization	24.2	13.8	3.5
Total	(41.4)	(51.8)	(62.1)
Trade names
Definite-lived intangible assets:
Gross carrying amount	1.5	1.5	1.6
Accumulated amortization	(0.3)	(0.2)	0.0
Net carrying amount	1.2	1.3	1.6
Favorable leases
Definite-lived intangible assets:
Gross carrying amount	47.6	48.1	50.2
Accumulated amortization	(15.8)	(9.1)	(2.4)
Net carrying amount	31.8	39.0	47.8
Trade names
Definite-lived intangible assets:
Indefinite-lived trade names	$ 404.8	$ 406.8	$ 418.2