Computation of Earnings Per Ordinary Share and Ordinary Share Equivalent (Details) - Computation of basic and diluted earnings per share (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Basic earnings per ordinary share and ordinary share equivalents:
Net income (loss) attributable to XL Group plc									$ 651,134	$ (474,760)	$ 603,550
Less: preference share dividends									0	0	(34,694)
Gain on redemption of Redeemable Series C preference ordinary shares									0	0	16,616
Net income (loss) attributable to ordinary shareholders	$ 81,448	$ 171,902	$ 221,156	$ 176,628	$ (515,537)	$ 42,398	$ 225,663	$ (227,284)	$ 651,134	$ (474,760)	$ 585,472
Weighted average ordinary shares outstanding									307,372	312,896	336,283
Basic earnings per ordinary share & ordinary share equivalents outstanding (in Dollars per share)	$ 0.27	$ 0.57	$ 0.71	$ 0.56	$ (1.62)	$ 0.14	$ 0.73	$ (0.73)	$ 2.12	$ (1.52)	$ 1.74
Diluted earnings per ordinary share and ordinary share equivalents:
Weighted average ordinary shares outstanding - basic									307,372	312,896	336,283
Impact of share based compensation and certain conversion features									2,910	0	1,426
Weighted average ordinary shares outstanding - diluted									310,282	312,896	337,709
Diluted earnings per ordinary share & ordinary share equivalents outstanding (in Dollars per share)	$ 0.27	$ 0.56	$ 0.71	$ 0.56	$ (1.62)	$ 0.14	$ 0.69	$ (0.73)	$ 2.10	$ (1.52)	$ 1.73
Dividends per share paid on ordinary shares									$ 0.44	$ 0.44	$ 0.40