Percentage of voting equity interests acquired at the acquisition date in the business combination.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=56956515&loc=d3e1392-128463

+ Details

Name:	us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of voting equity interests acquired in a business combination achieved in stages, including equity interests in the acquiree held by the acquirer immediately before the acquisition date and acquired at the acquisition date.

+ References

No definition available.

+ Details

Name:	us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeIncludingSubsequentAcquisitionPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

+ References

No definition available.

+ Details

Name:	us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Investing Activities
-URI http://asc.fasb.org/extlink&oid=6516133

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3213-108585

+ Details

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

- 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.

+ Details

Name:	us-gaap_RelatedPartyTransactionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The Company's percentage ownership in the subsidiaries that had debt outstanding at the balance sheet date.

+ References

No definition available.

+ Details

Name:	xlgroup_PercentageOwnershipOfSubsidiaries
Namespace Prefix:	xlgroup_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of independent investment management companies in which the Company is invested.

+ References

No definition available.

+ Details

Name:	xlgroup_RelatedPartyTransactionsNumberOfInvestmentManagementCompanies
Namespace Prefix:	xlgroup_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Related Party Transactions Number of Investment Technology Service Firms

+ References

No definition available.

+ Details

Name:	xlgroup_RelatedPartyTransactionsNumberofInvestmentTechnologyServiceFirms
Namespace Prefix:	xlgroup_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_BusinessAcquisitionAxis=xlgroup_NewEnergyRiskInc.Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=xlgroup_NewEnergyRiskInc.Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Related Party Transactions - Narrative (Details) $ in Millions		12 Months Ended
	Jul. 24, 2015 USD ($)	Dec. 31, 2015 management_company	Dec. 31, 2014 management_company
Related Party Transaction [Line Items]
Number of investment management companies		6	6
Percentage ownership of subsidiaries		100.00%	100.00%
Related Party Transactions Number of Investment Technology Service Firms		2	1
New Energy Risk Inc. [Member]
Related Party Transaction [Line Items]
Business acquisition, percentage of voting interests acquired	63.63%
Cash consideration \| $	$ 8.8
Business combination, step acquisition, equity interest in acquiree, including subsequent acquisition, percentage	94.79%
Noncontrolling interest, ownership percentage by noncontrolling owners	5.21%
New Energy Risk Inc. [Member]
Related Party Transaction [Line Items]
Percentage ownership of subsidiaries		100.00%