Goodwill and intangibles - Composition of Finite-Lived Intangibles (Details) - USD ($) $ in Millions	Apr. 29, 2017	Jan. 28, 2017	Apr. 30, 2016
Definite-lived intangible assets:
Gross carrying amount	$ 48.6	$ 49.0	$ 49.8
Accumulated amortization	(39.7)	(36.8)	(26.8)
Net carrying amount	8.9	12.2	23.0
Intangible assets, gross	451.6	453.8	457.2
Total intangible assets, net	411.9	417.0	430.4
Definite-lived intangible liabilities:
Gross carrying amount	(113.5)	(113.9)	(114.4)
Accumulated amortization	76.2	71.7	57.1
Total	(37.3)	(42.2)	(57.3)
Unfavorable leases
Definite-lived intangible liabilities:
Gross carrying amount	(47.9)	(48.3)	(48.8)
Accumulated amortization	41.4	38.2	27.7
Total	(6.5)	(10.1)	(21.1)
Unfavorable contracts
Definite-lived intangible liabilities:
Gross carrying amount	(65.6)	(65.6)	(65.6)
Accumulated amortization	34.8	33.5	29.4
Total	(30.8)	(32.1)	(36.2)
Trade names
Definite-lived intangible assets:
Gross carrying amount	1.4	1.4	1.5
Accumulated amortization	(0.8)	(0.8)	(0.6)
Net carrying amount	0.6	0.6	0.9
Favorable leases
Definite-lived intangible assets:
Gross carrying amount	47.2	47.6	48.3
Accumulated amortization	(38.9)	(36.0)	(26.2)
Net carrying amount	8.3	11.6	22.1
Trade names
Definite-lived intangible assets:
Indefinite-lived trade names	$ 403.0	$ 404.8	$ 407.4