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

Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e637-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e681-108580

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14A
-URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669686-108580

Name:	us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of the cumulative effect on retained earnings before related income tax effect.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=64853466&loc=d3e22663-107794

Name:	us-gaap_CumulativeEffectOnRetainedEarningsBeforeTax1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Amount of the related income tax effect of a cumulative effect on retained earnings.

Name:	us-gaap_CumulativeEffectOnRetainedEarningsTax1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Amount before tax and reclassification adjustments of other comprehensive income (loss).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14A
-URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669686-108580

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

Amount after tax and reclassification adjustments of other comprehensive income (loss).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21463-112644

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669619-108580

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669625-108580

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 55
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=84158357&loc=d3e1436-108581

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

Amount of tax expense (benefit) allocated to other comprehensive income (loss).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e640-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 20
-Section 45
-Paragraph 11
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=79507043&loc=d3e39076-109324

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

Amount before tax of reclassification adjustments of other comprehensive income (loss).

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

Cumulative Impact of Net Unrealized Gains Losses on Future Policy Benefit Reserve

No definition available.

Name:	xlgroup_CumulativeImpactofNetUnrealizedGainsLossesonFuturePolicyBenefitReserve
Namespace Prefix:	xlgroup_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount of the reclassification adjustment out of AOCI due to a new accounting pronouncement.

No definition available.

Name:	xlgroup_NewAccountingPronouncementorChangeinAccountingPrincipleEffectofAdoptionReclassificationOutofAOCI
Namespace Prefix:	xlgroup_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Other comprehensive income cumulative adjustment shadow liability future policy benefit reserve.

No definition available.

Name:	xlgroup_OtherComprehensiveIncomeCumulativeAdjustmentShadowLiabilityFuturePolicyBenefitReserve
Namespace Prefix:	xlgroup_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_AccumulatedOtherThanTemporaryImpairmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_AccumulatedTranslationAdjustmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_AccountingStandardsUpdate201601Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: