Schedule II - Condensed Financial Information of Registrant (Statement of Income and Comprehensive Income) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended			6 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	Jun. 30, 2010 XLIT Ltd.		Dec. 31, 2010 Xl Group PLC	Dec. 31, 2012 Xl Group PLC	Dec. 31, 2011 Xl Group PLC
Condensed Financial Statements Captions [Line Items]
Net investment income									$ 1,012,348	$ 1,137,769	$ 1,198,038	$ 44,636	[1]	$ 0	$ 5	$ 2
Realized investment gains (losses):
Net realized gains (losses) on investments sold									94,810	(28,187)	(65,670)	25,177	[1]	0	0	0
Other-than-temporary impairments on investments									(54,306)	(174,102)	(170,643)	(11,670)	[1]	0	0	0
Other-than-temporary impairments on investments transferred to (from) other comprehensive income									(26,406)	13,930	(34,490)	4	[1]	0	0	0
Net realized gains (losses) on investments									14,098	(188,359)	(270,803)	13,511	[1]	0	0	0
Net realized and unrealized (gains) losses on derivative instruments									5,221	(10,738)	(33,843)	(4,087)	[1]	0	0	0
Equity in net earnings of subsidiaries												384,311	[1]	275,629	662,280	(400,612)
Equity in net income (loss) in operating affiliates									114,314	103,039	172,474	2	[1]	0	0	0
Total revenues									7,230,480	6,696,803	6,398,582	438,373	[1]	275,629	662,285	(400,610)
Operating expenses									1,173,951	1,083,917	972,963	48,256	[1]	9,930	10,971	74,422
Exchange gains (losses)									10,546	(40,640)	(10,161)	1,003	[1]	34	165	(275)
Interest expense									172,205	205,592	213,643	51,431	[1]	0	15	3
Total expenses									6,521,874	7,117,765	5,713,836	100,690	[1]	9,964	11,151	74,150
Income loss before tax												337,683	[1]	265,665	651,134	(474,760)
Provision (benefit) for income tax									34,028	59,707	162,737	(202)	[1]	0	0	0
Net income (loss) attributable to XL Group plc									651,134	(474,760)	603,550	337,885	[1]	265,665	651,134	(474,760)
Dividends on Series C and Series E preference ordinary shares									0	0	(34,694)	(34,694)	[1]	0	0	0
Gain on redemption of Redeemable Series C preference ordinary shares									0	0	16,616	16,616	[1]	0	0	0
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	319,807	[1]	265,665	651,134	(474,760)
Impact of adoption of new authoritative embedded derivative guidance, net of taxes									0	0	31,917	0	[1]	31,917	0	0
Change in net unrealized gains (losses) on investments, net of tax									992,891	332,720	932,769	880,332	[1]	161,048	887,376	471,696
Change in OTTI losses recognized in other comprehensive income, net of tax									67,280	39,456	124,906	31,637	[1]	93,269	67,280	39,456
Change in underfunded pension liability									(9,985)	(2,622)	(2,619)	(3,567)	[1]	6,186	9,985	2,622
Change in value of cash flow hedge									439	439	439	(220)	[1]	(219)	(439)	(439)
Change in net unrealized gain (loss) on future policy benefit reserves									0	0	(3,714)	(3,714)	[1]	0	0	0
Foreign currency translation adjustments									(8,163)	(26,700)	50,953	(108,308)	[1]	159,261	(8,163)	(26,700)
Comprehensive income (loss)									1,588,081	7,509	1,846,812	1,141,619	[1]	705,193	1,588,081	7,509
Parenthetical information, dividends:
Dividends received from subsidiaries												$ 197,326		$ 448,400	$ 0	$ 183,029

[1] As part of the Redomestication on July 1, 2010, XL-Cayman became a wholly-owned subsidiary of XL-Ireland, and as such, certain of the above financial data with respect to periods prior to the Redomestication are not comparable for periods subsequent to the Redomestication.