Credit transaction, net - Narrative (Details) - USD ($) $ in Millions	1 Months Ended				3 Months Ended		6 Months Ended		12 Months Ended
	Jul. 31, 2018	May 31, 2018	Mar. 31, 2018	Oct. 28, 2017	Aug. 04, 2018	Jul. 29, 2017	Aug. 04, 2018	Jul. 29, 2017	Feb. 03, 2018
Debt Instrument [Line Items]
Credit transaction, net					$ (23.9)	$ 14.8	$ (167.0)	$ 14.8
Initial credit term (years)								7 years
Credit renewal term (years)								2 years
Percentage of eligible receivables purchased		30.00%
Sale of receivables, percentage of par			72.00%
Sale of receivables, percentage settled in cash			95.00%
Sale of receivables. percentage deferred until second anniversary			5.00%
Reversal of allowance on receivables previously held for sale							160.4	$ (20.7)
Proceeds from sale of in-house finance receivables	$ 445.5						445.5	0.0
Other
Debt Instrument [Line Items]
Transaction-related costs					4.5		6.6
Securitization Facility
Debt Instrument [Line Items]
Repayments of secured debt									$ 600.0
Consumer Portfolio Segment
Debt Instrument [Line Items]
Reversal of allowance on receivables previously held for sale							107.6	$ 20.7
Consumer Portfolio Segment | Sterling Jewelers
Debt Instrument [Line Items]
Reversal of allowance on receivables previously held for sale					(19.4)		(160.4)
Consumer Portfolio Segment | Other
Debt Instrument [Line Items]
Transaction-related costs					$ 4.5		$ 6.6
Sterling Jewelers, Inc. | Consumer Portfolio Segment
Debt Instrument [Line Items]
Net proceeds				$ 952.5
Genesis Financial Solution
Debt Instrument [Line Items]
Servicing agreement, term (years)				5 years