Significant Accounting Policies (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2012
New Accounting Pronouncement Cumulative Effect Of Change On Deferred Tax Liability	$ 21
New Accounting Pronouncement Cumulative Effect Of Change On Deferred Acquisition Costs	7
New Accounting Pronouncement Cumulative Effect Of Change On Equity Or Net Assets	$ 14

Amount of the cumulative effect of the change in accounting principle or new accounting pronouncement on retained earnings or other components of equity or net assets in the statement of financial position as of the beginning of the earliest period presented.

No definition available.

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