Acquisition and Disposals - Financial results (Details) - Catlin Group Limited $ in Thousands	2 Months Ended
Jun. 30, 2015 USD ($)
Business Combination Results of Operations [Line Items]
Total revenues	$ 709,800
Net income (loss) attributable to ordinary shareholders	$ 50,017

This element represents the amount of earnings or loss of the acquiree since the acquisition date included in the consolidated income statement for the reporting period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(1)

-URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463

+ Details

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

- Definition

This element represents the amount of revenue of the acquiree since the acquisition date included in the consolidated income statement for the reporting period.

+ References

+ Details

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

- Definition

[Line Items] for Business Combination Results of Operations [Table]

+ References

No definition available.

+ Details

Name:	xlgroup_BusinessCombinationResultsofOperationsLineItems
Namespace Prefix:	xlgroup_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_BusinessAcquisitionAxis=xlgroup_CatlinGroupLimitedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: