Name:	us-gaap_BusinessAcquisitionLineItems
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Amount of increase in assets, excluding financial assets, lacking physical substance with a definite life, from an acquisition.

No definition available.

Name:	us-gaap_FinitelivedIntangibleAssetsAcquired1
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Name:	us-gaap_GoodwillAcquiredDuringPeriod
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Amount of increase in assets, excluding financial assets and goodwill, lacking physical substance with an indefinite life, from an acquisition.

No definition available.

Name:	us-gaap_IndefinitelivedIntangibleAssetsAcquired
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Amount of expense for amortization of intangible assets arising from insurance contracts acquired in a business combination.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 20
-Section S99
-Paragraph 2
-Subparagraph (2)
-URI http://asc.fasb.org/extlink&oid=27015749&loc=d3e569990-122904

Name:	us-gaap_IntangiblesAssetsArisingFromInsuranceContractsAcquiredInBusinessCombinationAmortizationExpense1
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Unpaid Losses And Loss Expenses Adjustment Amortization Period

No definition available.

Name:	xlgroup_UnpaidLossesAndLossExpensesAdjustmentAmortizationPeriod
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Value of Business Acquired Adjustment, Amortization Period

No definition available.