Derivative Instruments Narrative (Details) (USD $)			3 Months Ended
Mar. 31, 2013 Contracts	Dec. 31, 2012	Mar. 31, 2013 Deposit liabilities	Mar. 31, 2012 Deposit liabilities
Derivative [Line Items]
Derivatives Number of Instruments Held	1
Fair Value Hedge Cumulative Reduction To Expense			$ 0	$ 2,400,000
Collateral posted to counterparty	0	12,130,000
Cash collateral held	$ 46,720,000	$ 0
Deficiency guarantee government backing percent	80.00%

The amount of the obligation to return cash collateral under master netting arrangements that have not been offset against net derivative instrument positions.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 8

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=d3e41678-113959

+ Details

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

- Definition

The amount of the right to reclaim cash collateral under master netting arrangements that have not been offset against net derivative instrument positions.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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

- Definition

Deficiency Guarantee Government Backing Percent

+ References

No definition available.

+ Details

Name:	xlgroup_DeficiencyGuaranteeGovernmentBackingPercent
Namespace Prefix:	xlgroup_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

-- None. No documentation exists for this element. --

+ References

No definition available.

+ Details

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

- Definition

The net decrease in interest expense for the period related to periodic coupon settlements between parties under interest rate swap agreements hedging certain financial instruments.

+ References

No definition available.

+ Details

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Namespace Prefix:	xlgroup_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration