Acquisition and Disposals - Impact of Life Retro arrangements (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015		Sep. 30, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Underwriting profit (loss)		$ 104,648	$ 139,138	$ 447,186		$ 371,444
Net investment income		225,146	226,430	656,863		692,392
Exchange (gains) losses		(11,661)	23,348	(49,425)		(8,234)
Other income and expenses	[1]	(4,420)	(3,058)	(12,292)		(6,410)
Net realized and unrealized gains (losses) on life retrocession embedded derivative		(7,903)	5,131	57,127		18,540
Net income (loss)		85,171	109,967	1,078,760		125,865
Change in adjustments related to future policy benefit reserves, net of tax		40,681	51,286	127,365		(423,179)
Change in cumulative translation adjustment		(22,394)	(11,813)	(20,714)		(25,295)
Comprehensive income (loss)		(121,092)	24,895	(529,376)		495,272
XL Re Life (SAC) Ltd
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Comprehensive income (loss)		0
Life Funds Withheld Assets
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net investment income		46,586	56,474	143,869		75,639
Net realized gains (losses) on investments sold		53,780	2,022	174,555		2,646
Net unrealized gains (losses) on investments, trading securities		(149)	0	(18,932)		0
OTTI on investments		(2,023)	(7,494)	(10,110)		(16,265)
Net realized and unrealized gains (losses) on life retrocession embedded derivative		(126,140)	(201,264)	(116,333)		(218,810)
Change in net unrealized gains (losses) on investments, net of tax		(33,569)	93,921	(317,500)		106,218
Life Funds Withheld Assets | XL Re Life (SAC) Ltd
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Underwriting profit (loss)		0	3,711	603	[2]	3,711
Net investment income		46,586	56,474	143,869		75,639
Net realized gains (losses) on investments sold		53,780	2,022	174,555		2,646
Net unrealized gains (losses) on investments, trading securities		(149)	0	(18,932)		0
OTTI on investments		(2,023)	(7,494)	(10,110)		(16,265)
Exchange (gains) losses		8,754	2,062	(5,932)		2,062
Other income and expenses		(121)	124	2,354		105
Net realized and unrealized gains (losses) on life retrocession embedded derivative		(126,140)	(201,264)	(116,333)		(218,810)
Net income (loss)		(19,313)	(144,365)	170,074		(150,912)
Change in net unrealized gains (losses) on investments, net of tax		(33,569)	93,921	(317,500)		106,218
Change in adjustments related to future policy benefit reserves, net of tax		40,681	51,286	127,365		51,286
Change in cumulative translation adjustment		12,201	2,869	20,664		(2,881)
Total changes to other comprehensive income as a result of Life Retro Arrangements		19,313	148,076	(169,471)		154,623
Comprehensive income (loss)		$ 0	$ 3,711	$ 603		$ 3,711

[1] Net fee income and other includes operating expenses from the Company's loss prevention consulting services business.

[2] The underwriting profit of $0.6 million relates to a premium adjustment during the nine months ended September 30, 2015 relating to the Life Retro Arrangements transaction. Excluding this transaction, the impact to comprehensive income relating to the Life Retro Arrangements was nil for the nine months ended September 30, 2015.