Share-based compensation - Narrative (Details)	12 Months Ended
Feb. 02, 2019 share_option_savings_plan shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of share option savings plans \| share_option_savings_plan	3
Omnibus Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Shares available for grant	3,575,000
Sharesave and Irish Sub-Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of allocated shares	1,000,000
Discount from market price	15.00%
Employee Share Savings Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Discount from market price	5.00%
Irish Sharesave Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	36 months
Number of allocated shares	1,250,000
Minimum \| Irish Sharesave Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	36 months
Maximum \| Irish Sharesave Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	42 months

Number of Share Option Savings Plans

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- Definition

The shares or units in an ESOP trust that have been assigned to individual participant accounts based on a known formula. IRS rules require allocations to be nondiscriminatory generally based on compensation, length of service, or a combination of both. For any particular participant such shares or units may be vested, unvested, or partially vested.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=109244661&loc=d3e17540-113929

+ Details

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- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

Discount rate from fair value on purchase date that participants pay for shares.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

+ Details

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- Details

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