Goodwill and intangibles - Composition of Finite-Lived Intangibles (Details) - USD ($) $ in Millions	Jul. 30, 2016	Jan. 30, 2016	Aug. 01, 2015
Definite-lived intangible assets:
Gross carrying amount	$ 49.2	$ 48.4	$ 49.1
Accumulated amortization	(30.0)	(22.8)	(16.1)
Net carrying amount	19.2	25.6	33.0
Intangible assets, gross	454.7	450.6	453.9
Total intangible assets, net	424.7	427.8	437.8
Definite-lived intangible liabilities:
Gross carrying amount	(114.0)	(113.3)	(113.9)
Accumulated amortization	62.0	51.8	41.0
Total	(52.0)	(61.5)	(72.9)
Unfavorable leases
Definite-lived intangible liabilities:
Gross carrying amount	(48.4)	(47.7)	(48.3)
Accumulated amortization	31.2	23.7	16.8
Total	(17.2)	(24.0)	(31.5)
Unfavorable contracts
Definite-lived intangible liabilities:
Gross carrying amount	(65.6)	(65.6)	(65.6)
Accumulated amortization	30.8	28.1	24.2
Total	(34.8)	(37.5)	(41.4)
Trade names
Definite-lived intangible assets:
Gross carrying amount	1.4	1.4	1.5
Accumulated amortization	(0.6)	(0.5)	(0.3)
Net carrying amount	0.8	0.9	1.2
Favorable leases
Definite-lived intangible assets:
Gross carrying amount	47.8	47.0	47.6
Accumulated amortization	(29.4)	(22.3)	(15.8)
Net carrying amount	18.4	24.7	31.8
Trade names
Definite-lived intangible assets:
Indefinite-lived trade names	$ 405.5	$ 402.2	$ 404.8