Derivative Instruments - Schedule of settlement of fair value hedges (Details) - Fair value hedges - Deposit liabilities - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2016	Sep. 30, 2015
Derivative [Line Items]
Cumulative reduction to interest expense	$ 110,914	$ 101,461
Remaining balance	$ 122,282	$ 131,734
Weighted average years remaining to maturity	20 years 4 months 24 days	22 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