Revenue recognition - Rollforward (Details) - Sterling Jewelers - USD ($) $ in Millions	3 Months Ended
May 05, 2018	Apr. 29, 2017
Movement in Deferred Revenue [Roll Forward]
ESP deferred revenue, beginning of period	$ 916.1	$ 905.6
Plans sold	96.0	96.6
Revenue recognized	(98.6)	(98.5)
ESP deferred revenue, end of period	$ 913.5	$ 903.7

Amount of increase in the standard and extended product warranty accrual from warranties issued.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph ((c)(3))
-URI http://asc.fasb.org/extlink&oid=68068213&loc=d3e12565-110249

Name:	us-gaap_ProductWarrantyAccrualWarrantiesIssued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration