Derivative Instruments (Details) - Schedule of settlement of fair value hedges (USD $) In Thousands, unless otherwise specified	3 Months Ended	1 Months Ended	3 Months Ended
Jun. 30, 2012 Notes Payable And Debt [Member] Fair Value Hedging Member	Jun. 30, 2011 Notes Payable And Debt [Member] Fair Value Hedging Member	Jul. 31, 2012 Deposit Liabilities [Member]	Jun. 30, 2012 Deposit Liabilities [Member] Fair Value Hedging Member	Jun. 30, 2011 Deposit Liabilities [Member] Fair Value Hedging Member
Derivative [Line Items]
Cumulative reduction to interest expense	$ 12,996	$ 7,432		$ 12,763	$ 5,646
Fair Value Hedge Remaining Balance	$ 8,628	$ 14,192		$ 136,722	$ 143,839
Weighted average years to maturity	2 years 2 months 12 days	2 years 10 months 24 days	16 years 1 month 6 days	32 years 4 months 24 days	35 years

Represents balance of the income received from or payment made to a third party in connection with the termination of a contract between the parties on a derivative contract formally designated in a hedging relationship remaining to be amortized.

No definition available.

Name:	xlgroup_FairValueHedgeRemainingBalance
Namespace Prefix:	xlgroup_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant