Receivables and Revenue Recognition - Revenue Recognition (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2018	Oct. 31, 2017
Disaggregation of Revenue [Line Items]
Net sales	$ 1,012.4	$ 976.2	$ 3,121.5	$ 2,835.4
Net sales related to merchandise credits and deferred revenue			30.0
Jewelry collections [Member]
Disaggregation of Revenue [Line Items]
Net sales	543.3	503.8	1,642.6	1,433.4
Engagement jewelry [Member]
Disaggregation of Revenue [Line Items]
Net sales	276.2	272.0	857.6	802.5
Designer jewelry [Member]
Disaggregation of Revenue [Line Items]
Net sales	111.1	120.9	367.5	358.1
All other [Member]
Disaggregation of Revenue [Line Items]
Net sales	$ 81.8	$ 79.5	$ 253.8	$ 241.4

Amount, including tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value-added and excise.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130539-203045

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130545-203045

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130543-203045

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