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, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Basic earnings per ordinary share and ordinary share equivalents:
Net income attributable to XL Group plc. (in Dollars)	$ (474,760)		$ 603,550		$ 74,991
Less: preference share dividends (1) (in Dollars)	0	[1]	(34,694)	[1]	(80,200)
Add: gain on redemption of the Redeemable Series C preference ordinary shares (in Dollars)	0		16,616		211,816
Net income (loss) attributable to ordinary shareholders (in Dollars)	$ (474,760)		$ 585,472		$ 206,607
Weighted average ordinary shares outstanding	312,896		336,283		340,612
Basic earnings per ordinary share & ordinary share equivalents outstanding (in Dollars per share)	$ (1.52)		$ 1.74		$ 0.61
Diluted earnings per ordinary share and ordinary share equivalents:
Weighted average ordinary shares outstanding – basic	312,896		336,283		340,612
Impact of share based compensation and certain conversion features	0		1,426		354
Weighted average ordinary shares outstanding – diluted	312,896		337,709		340,966
Diluted earnings per ordinary share & ordinary share equivalents outstanding (in Dollars per share)	$ (1.52)		$ 1.73		$ 0.61
Dividends per ordinary share (in Dollars per share)	$ 0.44		$ 0.40		$ 0.40

[1] During the first quarter of 2011, the Redeemable Series C preference ordinary shares were reclassified as Non-controlling interest - Redeemable Series C preference ordinary shares and Series E preference ordinary shares were reclassified as Non-controlling interest in equity of consolidated subsidiaries on the Company's consolidated balance sheet as a result of changes in ownership structure arising as part of the Company's redomestication of the ultimate parent holding company to Ireland as of July 1, 2010. Accordingly, preference share dividends declared are recorded as Non-controlling interests rather than as Preference share dividends within the consolidated statements of income from July 1, 2010 onwards. See Note 1, "Basis of Preparation and Consolidation" for additional details. During the third quarter of 2011, all outstanding Redeemable Series C preference ordinary shares were repurchased and canceled.