Acquisition and Disposals - Impact of Life Retro arrangements (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Underwriting profit (loss)	$ 139,207		$ 97,231
Net investment income	208,513		233,189
Exchange (gains) losses	(27,390)		(10,441)
Other income and expenses	(6,508)	[1]	(494)	[1]
Net realized and unrealized gains (losses) on life retrocession embedded derivative	16,521		1,810
Net income (loss)	73,671		291,476
Change in adjustments related to future policy benefit reserves, net of tax	60,356		(34,004)
Change in cumulative translation adjustment	36,103		(3,880)
Comprehensive income (loss)	220,712		210,004
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	50,419		0
Net realized gains (losses) on investments sold	52,738		0
Net unrealized gains (losses) on investments, trading securities	760		0
OTTI on investments	(5,209)		0
Net realized and unrealized gains (losses) on life retrocession embedded derivative	(229,367)		0
Change in net unrealized gains (losses) on investments, net of tax	37,115		0
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)	603
Net investment income	50,419
Net realized gains (losses) on investments sold	52,738
Net unrealized gains (losses) on investments, trading securities	760
OTTI on investments	(5,209)
Exchange (gains) losses	3,684
Other income and expenses	(1,298)
Net realized and unrealized gains (losses) on life retrocession embedded derivative	(229,367)
Net income (loss)	(127,670)
Change in net unrealized gains (losses) on investments, net of tax	37,115
Change in adjustments related to future policy benefit reserves, net of tax	60,356
Change in cumulative translation adjustment	30,802
Total changes to other comprehensive income as a result of Life Retro Arrangements	128,273
Comprehensive income (loss)	$ 603

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