Segment information - Summary of Activity by Segment (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 29, 2017	Jul. 30, 2016	Jul. 29, 2017	Jul. 30, 2016	Jan. 28, 2017
Segment Reporting Information [Line Items]
Reversal of allowance on receivables held for sale			$ (20.7)	$ 0.0
Sales	$ 1,399.6	$ 1,373.4	2,803.0	2,952.3
Operating income (loss)	135.6	119.9	250.9	331.9
Total assets	6,313.8	6,298.0	6,313.8	6,298.0	$ 6,597.8
Sterling Jewelers
Segment Reporting Information [Line Items]
Sales	868.1	839.4	1,739.1	1,819.8
Operating income (loss)	159.4	140.9	288.9	339.2
Total assets	3,807.1	3,699.5	3,807.1	3,699.5	4,015.4
Zale Jewelry
Segment Reporting Information [Line Items]
Sales	331.8	331.0	665.5	712.4
Operating income (loss)	1.2	0.5	3.3	18.8
Total assets	1,878.4	1,931.1	1,878.4	1,931.1	1,940.7
Piercing Pagoda
Segment Reporting Information [Line Items]
Sales	62.3	57.0	132.0	126.0
Operating income (loss)	1.0	(0.2)	4.2	7.6
Total assets	140.8	138.4	140.8	138.4	141.6
UK Jewelry
Segment Reporting Information [Line Items]
Sales	131.9	145.2	254.4	289.2
Operating income (loss)	2.3	1.7	(0.2)	3.0
Total assets	384.8	392.3	384.8	392.3	372.6
Other
Segment Reporting Information [Line Items]
Sales	5.5	0.8	12.0	4.9
Operating income (loss)	(28.3)	(23.0)	(45.3)	(36.7)
Total assets	$ 102.7	$ 136.7	102.7	136.7	$ 127.5
Consumer Portfolio Segment
Segment Reporting Information [Line Items]
Reversal of allowance on receivables held for sale			20.7	$ 0.0
Consumer Portfolio Segment | Sterling Jewelers
Segment Reporting Information [Line Items]
Reversal of allowance on receivables held for sale			20.7
Consumer Portfolio Segment | Other
Segment Reporting Information [Line Items]
Transaction costs			(5.9)
R2Net Inc. | Other
Segment Reporting Information [Line Items]
Acquisition related costs			$ 4.7