Computation of Earnings Per Ordinary Share and Ordinary Share Equivalent (Detail) - Computation of basic and diluted earnings per share (USD $) In Thousands, except Per Share data	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Basic earnings per ordinary share:
Net income (loss) attributable to XL Group plc	$ 225,663	$ 194,005	$ (1,621)	$ 337,885
Less: preference share dividends		(2,194)		(34,694)
Add: gain on redemption of Redeemable Series C preference ordinary shares				16,616
Net income available to ordinary shareholders	225,663	191,811	(1,621)	319,807
Weighted average ordinary shares outstanding – basic (in Shares)	309,184	342,056	310,325	342,049
Basic earnings per ordinary share (in Dollars per share)	$ 0.73	$ 0.56	$ (0.01)	$ 0.93
Diluted earnings per ordinary share:
Net income available to ordinary shareholders	225,663	191,811	(1,621)	319,807
Impact of assumed conversion of 10.75% Units	11,977
Net income available to ordinary shareholders including impact of assumed conversion of 10.75% Units	$ 237,640	$ 191,811	$ (1,621)	$ 319,807
Weighted average ordinary shares outstanding – basic (in Shares)	309,184	342,056	310,325	342,049
Impact of share based compensation and certain conversion features (in Shares)	32,805	822		732
Weighted average ordinary shares outstanding – diluted (in Shares)	341,989	342,878	310,325	342,781
Diluted earnings per ordinary share (in Dollars per share)	$ 0.69	$ 0.56	$ (0.01)	$ 0.93
Dividends per ordinary share (in Dollars per share)	$ 0.11	$ 0.10	$ 0.22	$ 0.20