SEGMENT INFORMATION (Tables)

12 Months Ended

Dec. 31, 2011

Schedule of Segment Reporting Information, by Segment [Table Text Block]

Year ended December 31, 2011: (U.S. dollars in thousands, except ratios)	Insurance			Reinsurance			Total P&C			Life Operations			Corporate			Total
Gross premiums written	$	4,824,665		$	2,073,619		$	6,898,284		$	394,555		$	—		$	7,292,839
Net premiums written		3,707,664			1,725,724			5,433,388			362,362			—			5,795,750
Net premiums earned		3,663,727			1,663,385			5,327,112			363,018			—			5,690,130
Net losses and loss expenses		(2,951,413	)		(1,126,978	)		(4,078,391	)		(535,074	)		—			(4,613,465	)
Acquisition costs		(461,965	)		(324,128	)		(786,093	)		(40,318	)		—			(826,411	)
Operating expenses (1)		(683,814	)		(176,167	)		(859,981	)		(9,311	)		—			(869,292	)
Underwriting profit (loss)	$	(433,465	)	$	36,112		$	(397,353	)	$	(221,685	)	$	—		$	(619,038	)
Net investment income								745,138			318,061			—			1,063,199
Net results from structured products (2)		10,976			12,053			23,029			—			—			23,029
Net fee income and other (3)		(16,370	)		3,903			(12,467	)		219			—			(12,248	)
Net realized gains (losses) on investments								(98,360	)		(89,999	)		—			(188,359	)
Contribution from P&C, Life Operations and Corporate							$	259,987		$	6,596		$	—		$	266,583
Corporate & other:
Net realized & unrealized gains (losses) on derivative instruments													$	(10,738	)	$	(10,738	)
Net income (loss) from investment fund affiliates and operating affiliates														103,039			103,039
Exchange gains (losses)														40,640			40,640
Corporate operating expenses														(159,158	)		(159,158	)
Interest expense (4)														(154,084	)		(154,084	)
Non-controlling interests														(70,877	)		(70,877	)
Impairment of goodwill (5)														(429,020	)		(429,020	)
Income taxes & other														(61,145	)		(61,145	)
Net income (loss) attributable to XL Group plc																$	(474,760	)
Ratios – P&C operations: (6)
Loss and loss expense ratio		80.6	%		67.8	%		76.6	%
Underwriting expense ratio		31.2	%		30.0	%		30.9	%
Combined ratio		111.8	%		97.8	%		107.5	%

Year ended December 31, 2010: (U.S. dollars in thousands, except ratios)	Insurance			Reinsurance			Total P&C			Life Operations			Corporate			Total
Gross premiums written	$	4,418,380		$	1,842,951		$	6,261,331		$	411,938		$	—		$	6,673,269
Net premiums written		3,461,150			1,538,438			4,999,588			382,075			—			5,381,663
Net premiums earned		3,529,138			1,501,999			5,031,137			382,924			—			5,414,061
Net losses and loss expenses		(2,505,502	)		(706,298	)		(3,211,800	)		(513,833	)		—			(3,725,633	)
Acquisition costs		(418,146	)		(321,008	)		(739,154	)		(49,104	)		—			(788,258	)
Operating expenses (1)		(642,103	)		(175,586	)		(817,689	)		(10,470	)		—			(828,159	)
Underwriting profit (loss)	$	(36,613	)	$	299,107		$	262,494		$	(190,483	)	$	—		$	72,011
Net investment income								803,358			313,172			—			1,116,530
Net results from structured products (2)		14,696			3,075			17,771			—			9,804			27,575
Net fee income and other (3)		(15,564	)		2,488			(13,076	)		249			2			(12,825	)
Net realized gains (losses) on investments								(206,877	)		(54,444	)		(9,482	)		(270,803	)
Contribution from P&C, Life Operations and Corporate							$	863,670		$	68,494		$	324		$	932,488
Corporate & other:
Net realized & unrealized gains (losses) on derivative instruments													$	(33,843	)	$	(33,843	)
Net income (loss) from investment fund affiliates and operating affiliates														172,474			172,474
Exchange gains (losses)														10,161			10,161
Corporate operating expenses														(90,686	)		(90,686	)
Interest expense (4)														(159,118	)		(159,118	)
Non-controlling interests														(39,831	)		(39,831	)
Loss on termination of guarantee														(23,500	)		(23,500	)
Income taxes & other														(164,595	)		(164,595	)
Net income (loss) attributable to XL Group plc																$	603,550
Ratios – P&C operations: (5)
Loss and loss expense ratio		71.0	%		47.0	%		63.8	%
Underwriting expense ratio		30.0	%		33.1	%		31.0	%
Combined ratio		101.0	%		80.1	%		94.8	%

Year ended December 31, 2009: (U.S. dollars in thousands, except ratios)	Insurance			Reinsurance			Total P&C			Life Operations			Corporate			Total
Gross premiums written	$	4,251,888		$	1,859,423		$	6,111,311		$	576,162		$	—		$	6,687,473
Net premiums written		3,273,380			1,470,332			4,743,712			532,852			—			5,276,564
Net premiums earned		3,559,793			1,591,946			5,151,739			555,101			—			5,706,840
Net losses and loss expenses		(2,399,747	)		(769,090	)		(3,168,837	)		(677,562	)		—			(3,846,399	)
Acquisition costs		(429,170	)		(346,699	)		(775,869	)		(77,689	)		—			(853,558	)
Operating expenses (1)		(689,131	)		(190,596	)		(879,727	)		(16,009	)		—			(895,736	)
Underwriting profit (loss)	$	41,745		$	285,561		$	327,306		$	(216,159	)	$	—		$	111,147
Net investment income								882,748			332,425			—			1,215,173
Net results from structured products (2)		16,660			26,374			43,034			—			16,609			59,643
Net fee income and other (3)		(14,241	)		6,209			(8,032	)		290			—			(7,742	)
Net realized gains (losses) on investments								(659,687	)		(232,375	)		(29,375	)		(921,437	)
Contribution from P&C, Life Operations and Corporate							$	585,369		$	(115,819	)	$	(12,766	)	$	456,784
Corporate & other:
Net realized & unrealized gains (losses) on derivative instruments													$	(33,647	)	$	(33,647	)
Net income (loss) from investment fund affiliates and operating affiliates														139,347			139,347
Exchange gains (losses)														(84,813	)		(84,813	)
Corporate operating expenses														(107,877	)		(107,877	)
Interest expense (4)														(172,764	)		(172,764	)
Non-controlling interest in net (income) loss of subsidiary														104			104
Loss on termination of guarantee														—			—
Income taxes & other														(122,143	)		(122,143	)
Net income (loss) attributable to XL Group plc																$	74,991
Ratios – P&C operations: (5)
Loss and loss expense ratio		67.4	%		48.3	%		61.5	%
Underwriting expense ratio		31.4	%		33.8	%		32.1	%
Combined ratio		98.8	%		82.1	%		93.6	%

Schedule Of Net Premiums Earned By Line Of Business [Text Block]

Year ended December 31, 2011: (U.S. dollars in thousands)	Insurance		Reinsurance			Life Operations		Total
P&C Operations:
Casualty – professional lines	$	1,287,230	$	213,949		$	—	$	1,501,179
Casualty – other lines		695,094		256,853			—		951,947
Property catastrophe		—		387,523			—		387,523
Other property		481,148		587,611			—		1,068,759
Marine, energy, aviation and satellite		528,454		130,855			—		659,309
Other specialty lines (1)		665,727		—			—		665,727
Other (2)		3,552		90,776			—		94,328
Structured indemnity		2,522		(4,182	)		—		(1,660	)
Total P&C Operations	$	3,663,727	$	1,663,385		$	—	$	5,327,112
Life Operations:
Other Life	$	—	$	—		$	230,786	$	230,786
Annuity		—		—			132,232		132,232
Total Life Operations	$	—	$	—		$	363,018	$	363,018
Total	$	3,663,727	$	1,663,385		$	363,018	$	5,690,130

Year ended December 31, 2010: (U.S. dollars in thousands)	Insurance		Reinsurance		Life Operations		Total
P&C Operations:
Casualty – professional lines	$	1,316,172	$	222,720	$	—	$	1,538,892
Casualty – other lines		611,674		219,154		—		830,828
Property catastrophe		—		323,588		—		323,588
Other property		416,806		534,422		—		951,228
Marine, energy, aviation and satellite		540,319		88,855		—		629,174
Other specialty lines (1)		621,839		—		—		621,839
Other (2)		7,577		112,303		—		119,880
Structured indemnity		14,751		957		—		15,708
Total P&C Operations	$	3,529,138	$	1,501,999	$	—	$	5,031,137
Life Operations:
Other Life	$	—	$	—	$	255,905	$	255,905
Annuity		—		—		127,019		127,019
Total Life Operations	$	—	$	—	$	382,924	$	382,924
Total	$	3,529,138	$	1,501,999	$	382,924	$	5,414,061

Year ended December 31, 2009: (U.S. dollars in thousands)	Insurance		Reinsurance		Life Operations		Total
P&C Operations:
Casualty – professional lines	$	1,276,005	$	196,624	$	—	$	1,472,629
Casualty – other lines		655,126		257,610		—		912,736
Property catastrophe		2,396		312,780		—		315,176
Other property		424,045		560,379		—		984,424
Marine, energy, aviation and satellite		546,806		83,532		—		630,338
Other specialty lines (1)		634,436		—		—		634,436
Other (2)		12,217		172,588		—		184,805
Structured indemnity		8,762		8,433		—		17,195
Total P&C Operations	$	3,559,793	$	1,591,946	$	—	$	5,151,739
Life Operations:
Other Life	$	—	$	—	$	422,594	$	422,594
Annuity		—		—		132,507		132,507
Total Life Operations	$	—	$	—	$	555,101	$	555,101
Total	$	3,559,793	$	1,591,946	$	555,101	$	5,706,840

Net Premiums Written By Geographical Location [Text Block]

P&C operations:
(U.S. dollars in thousands)	2011		2010		2009
Bermuda	$	572,825	$	561,514	$	545,965
United States		2,320,274		2,143,240		2,342,656
Europe and other		2,540,289		2,294,834		1,855,091
Total P&C operations	$	5,433,388	$	4,999,588	$	4,743,712
Life Operations:
(U.S. dollars in thousands)
Bermuda	$	75,219	$	79,033	$	80,498
United States		—		—		31,478
Europe and other		287,143		303,042		420,876
Total Life Operations	$	362,362	$	382,075	$	532,852
Total	$	5,795,750	$	5,381,663	$	5,276,564