Guarantor Financial Information Income Statement (Details) - USD ($) $ in Thousands			3 Months Ended		9 Months Ended
		Jul. 07, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017		Sep. 30, 2016
Revenues:
Net premiums earned			$ 2,620,902	$ 2,434,037	$ 7,660,610		$ 7,320,859
Net investment income			202,779	209,771	611,985		631,045
Total net realized gains (losses) on investments			43,274	143,676	137,188		341,043
Net realized and unrealized gains (losses) on derivative instruments			(20,434)	5,490	(28,409)		2,774
Income (loss) from investment fund affiliates			57,656	12,156	126,735		20,756
Fee income and other			11,469	8,600	35,355		27,724
Total revenues			2,883,984	2,588,120	8,427,105		7,652,769
Expenses:
Net losses and loss expenses incurred			3,066,723	1,491,803	6,179,262		4,506,674
Claims and policy benefits			10,592	5,875	25,478		16,294
Acquisition costs			445,685	403,888	1,315,138		1,227,675
Operating expenses			409,356	508,458	1,350,172		1,546,360
Exchange (gains) losses			55,017	(1,695)	46,038		(54,614)
(Gain) Loss on sale of subsidiary			0	(3,670)	0		(3,670)
Extinguishment of debt		$ 1,582	1,582	0	1,582		0
Interest expense			33,919	49,445	138,648		157,486
Total expenses			4,022,874	2,454,104	9,056,318		7,396,205
Income (loss) before income tax and income (loss) from operating affiliates			(1,138,890)	134,016	(629,213)		256,564
Income (loss) from operating affiliates			4,872	12,410	61,185		46,478
Equity in net earnings (losses) of subsidiaries			0	0	0		0
Provision (benefit) for income tax			(60,132)	17,749	(18,034)		42,511
Net income (loss)			(1,073,886)	128,677	(549,994)		260,531
Non-controlling interests			(30,197)	58,076	39,232		124,263
Net income (loss) attributable to common shareholders			(1,043,689)	70,601	(589,226)		136,268
Comprehensive income (loss)			(995,926)	181,819	(335,844)		969,457
Life Funds Withheld Assets
Revenues:
Net investment income			30,796	38,937	95,599		119,643
Net realized and unrealized gains (losses) on derivative instruments			(31,662)	(225,610)	(116,359)		(691,432)
Consolidating Adjustments and Eliminations
Revenues:
Net premiums earned			0	0	0		0
Net investment income			(545)	910	(614)		1,896
Total net realized gains (losses) on investments			213	49	213		1,949
Net realized and unrealized gains (losses) on derivative instruments			0	0	0		0
Income (loss) from investment fund affiliates			0	0	0		0
Fee income and other			0	0	0		0
Total revenues			(332)	959	(401)		3,845
Expenses:
Net losses and loss expenses incurred			0	0	0		0
Claims and policy benefits			0	0	0		0
Acquisition costs			0	0	0		0
Operating expenses			0	0	0		0
Exchange (gains) losses			0	0	0		0
(Gain) Loss on sale of subsidiary				0			0
Extinguishment of debt			0		0
Interest expense			0	0	0		0
Total expenses			0	0	0		0
Income (loss) before income tax and income (loss) from operating affiliates			(332)	959	(401)		3,845
Income (loss) from operating affiliates			0	0	0		0
Equity in net earnings (losses) of subsidiaries			2,043,981	(254,725)	942,567		(494,796)
Provision (benefit) for income tax			0	0	0		0
Net income (loss)			2,043,649	(253,766)	942,166		(490,951)
Non-controlling interests			(332)	(75)	(401)		(251)
Net income (loss) attributable to common shareholders			2,043,981	(253,691)	942,567		(490,700)
Comprehensive income (loss)			1,915,721	(476,127)	435,803		(2,157,078)
Consolidating Adjustments and Eliminations | Life Funds Withheld Assets
Revenues:
Net realized and unrealized gains (losses) on derivative instruments			0	0	0		0
XL- Bermuda/Ireland
Revenues:
Net premiums earned	[1]		0	0	0		0
Net investment income	[1]		58	75	152		251
Total net realized gains (losses) on investments	[1]		(213)	0	(213)		0
Net realized and unrealized gains (losses) on derivative instruments	[1]		0	0	0		0
Income (loss) from investment fund affiliates	[1]		0	0	0		0
Fee income and other	[1]		0	0	0		0
Total revenues	[1]		(155)	75	(61)		251
Expenses:
Net losses and loss expenses incurred	[1]		0	0	0		0
Claims and policy benefits	[1]		0	0	0		0
Acquisition costs	[1]		0	0	0		0
Operating expenses	[1]		407	19,979	43,976		22,753
Exchange (gains) losses	[1]		738	(180)	1,850		(633)
(Gain) Loss on sale of subsidiary	[1]			0			0
Extinguishment of debt			0		0	[1]
Interest expense	[1]		0	10	0		(5)
Total expenses	[1]		1,145	19,809	45,826		22,115
Income (loss) before income tax and income (loss) from operating affiliates	[1]		(1,300)	(19,734)	(45,887)		(21,864)
Income (loss) from operating affiliates	[1]		0	0	0		0
Equity in net earnings (losses) of subsidiaries	[1]		(1,042,389)	90,335	(543,339)		157,512
Provision (benefit) for income tax	[1]		0	0	0		(620)
Net income (loss)	[1]		(1,043,689)	70,601	(589,226)		136,268
Non-controlling interests	[1]		0	0	0		0
Net income (loss) attributable to common shareholders	[1]		(1,043,689)	70,601	(589,226)		136,268
Comprehensive income (loss)	[1]		(995,926)	181,819	(335,844)		969,457
XL- Bermuda/Ireland | Life Funds Withheld Assets
Revenues:
Net realized and unrealized gains (losses) on derivative instruments	[1]		0	0	0		0
XLIT
Revenues:
Net premiums earned			0	0	0		0
Net investment income			2,394	2,463	6,810		7,344
Total net realized gains (losses) on investments			25	370	694		1,623
Net realized and unrealized gains (losses) on derivative instruments			0	0	0		0
Income (loss) from investment fund affiliates			0	0	0		0
Fee income and other			0	0	0		0
Total revenues			2,419	2,833	7,504		8,967
Expenses:
Net losses and loss expenses incurred			0	0	0		0
Claims and policy benefits			0	0	0		0
Acquisition costs			0	0	0		0
Operating expenses			724	5,625	2,384		8,191
Exchange (gains) losses			7,020	32	7,046		(140)
(Gain) Loss on sale of subsidiary				0			0
Extinguishment of debt			1,582		1,582
Interest expense			39,897	35,320	110,321		105,666
Total expenses			49,223	40,977	121,333		113,717
Income (loss) before income tax and income (loss) from operating affiliates			(46,804)	(38,144)	(113,829)		(104,750)
Income (loss) from operating affiliates			0	0	0		0
Equity in net earnings (losses) of subsidiaries			(1,001,592)	164,390	(399,228)		337,284
Provision (benefit) for income tax			0	0	0		0
Net income (loss)			(1,048,396)	126,246	(513,057)		232,534
Non-controlling interests			(6,007)	35,911	30,282		75,022
Net income (loss) attributable to common shareholders			(1,042,389)	90,335	(543,339)		157,512
Comprehensive income (loss)			(994,626)	201,553	(289,957)		990,701
XLIT | Life Funds Withheld Assets
Revenues:
Net realized and unrealized gains (losses) on derivative instruments			0	0	0		0
Other XL Subsidiaries
Revenues:
Net premiums earned			2,620,902	2,434,037	7,660,610		7,320,859
Net investment income			200,872	206,323	605,637		621,554
Total net realized gains (losses) on investments			43,249	143,257	136,494		337,471
Net realized and unrealized gains (losses) on derivative instruments			(20,434)	5,490	(28,409)		2,774
Income (loss) from investment fund affiliates			57,656	12,156	126,735		20,756
Fee income and other			11,469	8,600	35,355		27,724
Total revenues			2,882,052	2,584,253	8,420,063		7,639,706
Expenses:
Net losses and loss expenses incurred			3,066,723	1,491,803	6,179,262		4,506,674
Claims and policy benefits			10,592	5,875	25,478		16,294
Acquisition costs			445,685	403,888	1,315,138		1,227,675
Operating expenses			408,225	482,854	1,303,812		1,515,416
Exchange (gains) losses			47,259	(1,547)	37,142		(53,841)
(Gain) Loss on sale of subsidiary				(3,670)			(3,670)
Extinguishment of debt			0		0
Interest expense			(5,978)	14,115	28,327		51,825
Total expenses			3,972,506	2,393,318	8,889,159		7,260,373
Income (loss) before income tax and income (loss) from operating affiliates			(1,090,454)	190,935	(469,096)		379,333
Income (loss) from operating affiliates			4,872	12,410	61,185		46,478
Equity in net earnings (losses) of subsidiaries			0	0	0		0
Provision (benefit) for income tax			(60,132)	17,749	(18,034)		43,131
Net income (loss)			(1,025,450)	185,596	(389,877)		382,680
Non-controlling interests			(23,858)	22,240	9,351		49,492
Net income (loss) attributable to common shareholders			(1,001,592)	163,356	(399,228)		333,188
Comprehensive income (loss)			(953,829)	274,574	(145,846)		1,166,377
Other XL Subsidiaries | Life Funds Withheld Assets
Revenues:
Net realized and unrealized gains (losses) on derivative instruments			$ (31,662)	$ (225,610)	$ (116,359)		$ (691,432)

[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 be distributed to XL Group upon completion of the liquidation.