Derivative Instruments - Impact of life retro arrangements (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2016		Mar. 31, 2015
Derivative [Line Items]
Underwriting profit (loss)		$ 172,037		$ 139,207
Net investment income		205,886		208,513
Foreign Currency Transaction Gain (Loss), before Tax		33,819		(27,390)
Other income and expenses		(2,723)	[1]	(6,508)
Net realized and unrealized gains (losses) on life retrocession embedded derivative		(3,622)		16,521
Net income (loss)		83,028		73,671
Change in adjustments related to future policy benefit reserves, net of tax		17,035		60,356
Foreign currency translation adjustments, net of tax		(16,439)		36,103
Comprehensive income (loss)		407,941		220,712
Life Funds Withheld Assets
Derivative [Line Items]
Net investment income		41,560		50,419
Net realized gains (losses) on investments sold		34,416		52,738
Net unrealized gains (losses) on investments, trading securities		69,096		760
Other-than-temporary impairments on investments		(2,346)		(5,209)
Net realized and unrealized gains (losses) on life retrocession embedded derivative		(236,080)		(229,367)
Change in net unrealized gains (losses) on investments, net of tax		51,990		37,115
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		603
Net investment income		41,560		50,419
Net realized gains (losses) on investments sold		34,416		52,738
Net unrealized gains (losses) on investments, trading securities		69,096		760
Other-than-temporary impairments on investments		(2,346)		(5,209)
Foreign Currency Transaction Gain (Loss), before Tax		11,119		3,684
Other income and expenses		(146)		(1,298)
Net realized and unrealized gains (losses) on life retrocession embedded derivative		(236,080)		(229,367)
Net income (loss)		(82,381)		(127,670)
Change in net unrealized gains (losses) on investments, net of tax		51,990		37,115
Change in adjustments related to future policy benefit reserves, net of tax		17,035		60,356
Foreign currency translation adjustments, net of tax		13,356		30,802
Change In Other Comprehensive Income Life Retro Arrangements		82,381		128,273
Comprehensive income (loss)		$ 0		$ 603

[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 three months ended March 31, 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 three months ended March 31, 2015.