Guarantor Financial Information - Income Statement (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016		Dec. 31, 2015	Dec. 31, 2014
Condensed Statement of Income Captions [Line Items]
Net premiums earned	$ 9,777,934		$ 8,226,425	$ 5,895,070
Net investment income	827,133		872,370	918,625
Total net realized gains (losses) on investments	372,138		202,178	107,462
Net realized and unrealized gains (losses) on derivative instruments	2,521		53,123	29,886
Income (loss) from investment fund affiliates	70,758		73,320	95,816
Fee income and other	35,692		33,201	43,630
Total revenues	10,546,086		9,308,926	6,602,267
Net losses and loss expenses incurred	6,072,835		4,766,200	3,258,393
Claims and policy benefits	28,244		115,997	242,963
Acquisition costs	1,620,671		1,317,448	738,118
Operating expenses	2,063,362		1,966,939	1,341,315
Exchange (gains) losses	(9,578)		22,504	(37,568)
Loss (gain) sale of subsidiaries	(7,088)		0	666,423
Extinguishment of debt	0		5,592	0
Interest expense	209,763		205,215	134,106
Total expenses	9,978,209		8,399,895	6,343,750
Income (loss) before income tax and income (loss) from operating affiliates	567,877		909,031	258,517
Income (loss) from operating affiliates	44,397		44,740	107,218
Gain on sale of operating affiliate	0		340,407	0
Equity in net earnings (losses) of subsidiaries	0		0	0
Provision (benefit) for income tax	42,129		(19,161)	96,897
Net income (loss)	570,145		1,313,339	268,838
Non-controlling interests	129,177		106,187	80,498
Net income (loss) attributable to common shareholders	440,968		1,207,152	188,340
Comprehensive income (loss)	469,898		409,310	936,141
Life Funds Withheld Assets
Condensed Statement of Income Captions [Line Items]
Net investment income	154,751		187,489	129,575
Net realized and unrealized gains (losses) on derivative instruments	(540,090)		(151,691)	(488,222)
Consolidating Adjustments and Eliminations
Condensed Statement of Income Captions [Line Items]
Net premiums earned	0		0	0
Net investment income	(436)		3,836	8,483
Total net realized gains (losses) on investments	0		(8,765)	(22,229)
Net realized and unrealized gains (losses) on derivative instruments	0		0	0
Income (loss) from investment fund affiliates	0		0	0
Fee income and other	0		0	0
Total revenues	(436)		(4,929)	(13,746)
Net losses and loss expenses incurred	0		0	0
Claims and policy benefits	0		0	0
Acquisition costs	0		0	0
Operating expenses	0		0	0
Exchange (gains) losses	0		0	0
Loss (gain) sale of subsidiaries	0			0
Extinguishment of debt			0
Interest expense	0		0	0
Total expenses	0		0	0
Income (loss) before income tax and income (loss) from operating affiliates	(436)		(4,929)	(13,746)
Income (loss) from operating affiliates	0		0	0
Gain on sale of operating affiliate			0
Equity in net earnings (losses) of subsidiaries	(1,276,926)		(2,703,013)	(548,445)
Provision (benefit) for income tax	0		0	0
Net income (loss)	(1,277,362)		(2,707,942)	(562,191)
Non-controlling interests	(436)		0	0
Net income (loss) attributable to common shareholders	(1,276,926)		(2,707,942)	(562,191)
Comprehensive income (loss)	(1,334,786)		(1,112,258)	(2,057,793)
Consolidating Adjustments and Eliminations | Life Funds Withheld Assets
Condensed Statement of Income Captions [Line Items]
Net realized and unrealized gains (losses) on derivative instruments	0		0	0
XL-Bermuda
Condensed Statement of Income Captions [Line Items]
Net premiums earned	0	[1]	0	0
Net investment income	436	[1]	169	275
Total net realized gains (losses) on investments	0	[1]	0	0
Net realized and unrealized gains (losses) on derivative instruments	0	[1]	0	0
Income (loss) from investment fund affiliates	0	[1]	0	0
Fee income and other	0	[1]	0	0
Total revenues	436	[1]	169	275
Net losses and loss expenses incurred	0	[1]	0	0
Claims and policy benefits	0	[1]	0	0
Acquisition costs	0	[1]	0	0
Operating expenses	93,247	[1]	46,340	9,646
Exchange (gains) losses	(1,106)	[1]	(345)	127
Loss (gain) sale of subsidiaries	0	[1]		0
Extinguishment of debt			0
Interest expense	(4)	[1]	11	5
Total expenses	92,137	[1]	46,006	9,778
Income (loss) before income tax and income (loss) from operating affiliates	(91,701)	[1]	(45,837)	(9,503)
Income (loss) from operating affiliates	0	[1]	0	0
Gain on sale of operating affiliate			0
Equity in net earnings (losses) of subsidiaries	532,049	[1]	1,253,609	197,843
Provision (benefit) for income tax	(620)	[1]	620	0
Net income (loss)	440,968	[1]	1,207,152	188,340
Non-controlling interests	0	[1]	0	0
Net income (loss) attributable to common shareholders	440,968	[1]	1,207,152	188,340
Comprehensive income (loss)	469,898	[1]	409,310	936,141
XL-Bermuda | Life Funds Withheld Assets
Condensed Statement of Income Captions [Line Items]
Net realized and unrealized gains (losses) on derivative instruments	0	[1]	0	0
XL-Cayman
Condensed Statement of Income Captions [Line Items]
Net premiums earned	0		0	0
Net investment income	9,135		9,363	20,256
Total net realized gains (losses) on investments	1,918		13,814	27,541
Net realized and unrealized gains (losses) on derivative instruments	0		12,363	0
Income (loss) from investment fund affiliates	0		0	0
Fee income and other	0		0	0
Total revenues	11,053		35,540	47,797
Net losses and loss expenses incurred	0		0	0
Claims and policy benefits	0		0	0
Acquisition costs	0		0	0
Operating expenses	4,985		10,565	13,102
Exchange (gains) losses	(343)		20	168
Loss (gain) sale of subsidiaries	0			0
Extinguishment of debt			0
Interest expense	140,644		143,330	110,323
Total expenses	145,286		153,915	123,593
Income (loss) before income tax and income (loss) from operating affiliates	(134,233)		(118,375)	(75,796)
Income (loss) from operating affiliates	0		0	0
Gain on sale of operating affiliate			0
Equity in net earnings (losses) of subsidiaries	744,877		1,449,404	350,602
Provision (benefit) for income tax	0		245	(212)
Net income (loss)	610,644		1,330,784	275,018
Non-controlling interests	78,595		77,175	77,175
Net income (loss) attributable to common shareholders	532,049		1,253,609	197,843
Comprehensive income (loss)	560,979		455,767	945,644
XL-Cayman | Life Funds Withheld Assets
Condensed Statement of Income Captions [Line Items]
Net realized and unrealized gains (losses) on derivative instruments	0		0	0
Other XL-Bermuda Subsidiaries
Condensed Statement of Income Captions [Line Items]
Net premiums earned	9,777,934		8,226,425	5,895,070
Net investment income	817,998		859,002	889,611
Total net realized gains (losses) on investments	370,220		197,129	102,150
Net realized and unrealized gains (losses) on derivative instruments	2,521		40,760	29,886
Income (loss) from investment fund affiliates	70,758		73,320	95,816
Fee income and other	35,692		33,201	43,630
Total revenues	10,535,033		9,278,146	6,567,941
Net losses and loss expenses incurred	6,072,835		4,766,200	3,258,393
Claims and policy benefits	28,244		115,997	242,963
Acquisition costs	1,620,671		1,317,448	738,118
Operating expenses	1,965,130		1,910,034	1,318,567
Exchange (gains) losses	(8,129)		22,829	(37,863)
Loss (gain) sale of subsidiaries	(7,088)			666,423
Extinguishment of debt			5,592
Interest expense	69,123		61,874	23,778
Total expenses	9,740,786		8,199,974	6,210,379
Income (loss) before income tax and income (loss) from operating affiliates	794,247		1,078,172	357,562
Income (loss) from operating affiliates	44,397		44,740	107,218
Gain on sale of operating affiliate			340,407
Equity in net earnings (losses) of subsidiaries	0		0	0
Provision (benefit) for income tax	42,749		(20,026)	97,109
Net income (loss)	795,895		1,483,345	367,671
Non-controlling interests	51,018		29,012	3,323
Net income (loss) attributable to common shareholders	744,877		1,454,333	364,348
Comprehensive income (loss)	773,807		656,491	1,112,149
Other XL-Bermuda Subsidiaries | Life Funds Withheld Assets
Condensed Statement of Income Captions [Line Items]
Net realized and unrealized gains (losses) on derivative instruments	$ (540,090)		$ (151,691)	$ (488,222)

[1] Results for the period include XL-Ireland, which prior to the Redomestication was the ultimate parent and is now in liquidation proceedings as outlined in Note 1, "Significant Accounting Policies." The Company expects the net assets of XL-Ireland to ultimately be distributed to XL-Bermuda upon completion of the liquidation.