Derivative Instruments - Impact of life retro arrangements (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Derivative [Line Items]
Underwriting profit (loss)		$ 97,691	$ 203,331	$ 269,728	$ 342,538
Net investment income		215,388	223,204	421,274	431,717
Foreign exchange (gains) losses		(19,100)	10,374	(52,919)	37,764
Other income and expenses	[1]	(2,330)	(1,364)	(5,053)	(7,872)
Net realized and unrealized gains (losses) on life retrocession embedded derivative		906	48,509	(2,716)	65,030
Net income (loss)		48,826	919,918	131,854	993,589
Change in adjustments related to future policy benefit reserves, net of tax		8,727	26,328	25,762	86,684
Foreign currency translation adjustments, net of tax		63,343	(34,423)	46,904	1,680
Comprehensive income (loss)		314,030	(628,996)	721,971	(408,284)
Life Funds Withheld Assets
Derivative [Line Items]
Net investment income		39,146	46,864	80,706	97,283
Net realized gains (losses) on investments sold		30,114	68,037	64,530	120,775
Net unrealized gains (losses) on investments, trading securities		55,287	(19,543)	124,383	(18,783)
Other-than-temporary impairments on investments		(252)	(2,878)	(2,598)	(8,087)
Net realized and unrealized gains (losses) on life retrocession embedded derivative		(229,742)	239,174	(465,822)	9,807
Change in net unrealized gains (losses) on investments, net of tax		77,248	(321,046)	129,238	(283,931)
XL Re Life (SAC) Ltd
Derivative [Line Items]
Comprehensive income (loss)				0
XL Re Life (SAC) Ltd | Life Funds Withheld Assets
Derivative [Line Items]
Underwriting profit (loss)	[2]	0	0	0	603
Net investment income		39,146	46,864	80,706	97,283
Net realized gains (losses) on investments sold		30,114	68,037	64,530	120,775
Net unrealized gains (losses) on investments, trading securities		55,287	(19,543)	124,383	(18,783)
Other-than-temporary impairments on investments		(252)	(2,878)	(2,598)	(8,087)
Foreign exchange (gains) losses		(6,755)	(18,370)	4,364	(14,686)
Other income and expenses		(24)	3,773	(170)	2,475
Net realized and unrealized gains (losses) on life retrocession embedded derivative		(229,742)	239,174	(465,822)	9,807
Net income (loss)		(112,226)	317,057	(194,607)	189,387
Change in net unrealized gains (losses) on investments, net of tax		77,248	(321,046)	129,238	(283,931)
Change in adjustments related to future policy benefit reserves, net of tax		8,727	26,328	25,762	86,684
Foreign currency translation adjustments, net of tax		26,251	(22,339)	39,607	8,463
Change In Other Comprehensive Income Life Retro Arrangements		112,226	(317,057)	194,607	(188,784)
Comprehensive income (loss)		$ 0	$ 0	$ 0	$ 603

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

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