Derivative Instruments - Schedule of settlement of fair value hedges (Details) - Fair value hedges - Deposit liabilities - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2016	Mar. 31, 2015
Derivative [Line Items]
Cumulative reduction to interest expense	$ 106,056	$ 97,705
Remaining balance	$ 127,139	$ 135,490
Weighted average years remaining to maturity	21 years 2 months 12 days	22 years 2 months 12 days

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