Guarantor Financial Information Income Statement (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Revenues:
Net premiums earned		$ 2,600,288	$ 2,522,791
Net investment income		218,481	200,532
Total realized investment gains (losses)		(83,355)	37,286
Net realized and unrealized gains (losses) on derivative instruments		4,221	(7,069)
Income (loss) from investment affiliates		45,669	38,261
Fee income and other		6,717	13,661
Total revenues		2,814,942	2,755,361
Expenses:
Net losses and loss expenses incurred		1,622,006	1,583,456
Claims and policy benefits		10,307	7,291
Acquisition costs		463,827	435,869	[1]
Operating expenses		472,563	468,038
Foreign exchange (gains) losses		9,841	(3,336)
Interest expense		53,545	50,711
Total expenses		2,632,089	2,542,029
Income (loss) before income tax expense and income (loss) from operating affiliate		182,853	213,332
Income (loss) from operating affiliates		10,282	13,609
Equity in net earnings (losses) of subsidiaries		0	0
Provision (benefit) for income tax		31,902	13,092
Net income (loss)		161,233	213,849
Non-controlling interests		8,585	61,006
Net income (loss) attributable to common shareholders		152,648	152,843
Comprehensive income (loss)		(206,575)	282,271
Life Funds Withheld Assets
Revenues:
Net investment income		30,398	33,364
Net realized and unrealized gains (losses) on derivative instruments		22,921	(50,101)
Consolidating Adjustments and Eliminations
Revenues:
Net premiums earned		0	0
Net investment income		0	(83)
Total realized investment gains (losses)		0	0
Net realized and unrealized gains (losses) on derivative instruments		0	0
Income (loss) from investment affiliates		0	0
Fee income and other		0	0
Total revenues		0	(83)
Expenses:
Net losses and loss expenses incurred		0	0
Claims and policy benefits		0	0
Acquisition costs		0	0
Operating expenses		0	0
Foreign exchange (gains) losses		0	0
Interest expense		0	0
Total expenses		0	0
Income (loss) before income tax expense and income (loss) from operating affiliate		0	(83)
Income (loss) from operating affiliates		0	0
Equity in net earnings (losses) of subsidiaries		(419,046)	(408,642)
Provision (benefit) for income tax		0	0
Net income (loss)		(419,046)	(408,725)
Non-controlling interests		0	(83)
Net income (loss) attributable to common shareholders		(419,046)	(408,642)
Comprehensive income (loss)		299,400	(667,498)
Consolidating Adjustments and Eliminations | Life Funds Withheld Assets
Revenues:
Net realized and unrealized gains (losses) on derivative instruments		0	0
XL-Group/XL-Ireland
Revenues:
Net premiums earned	[2]	0	0
Net investment income	[2]	8	83
Total realized investment gains (losses)	[2]	0	0
Net realized and unrealized gains (losses) on derivative instruments	[2]	0	0
Income (loss) from investment affiliates	[2]	0	0
Fee income and other	[2]	4	0
Total revenues	[2]	12	83
Expenses:
Net losses and loss expenses incurred	[2]	0	0
Claims and policy benefits	[2]	0	0
Acquisition costs	[2]	0	0
Operating expenses	[2]	30,862	16,180
Foreign exchange (gains) losses	[2]	1,270	176
Interest expense	[2]	0	0
Total expenses	[2]	32,132	16,356
Income (loss) before income tax expense and income (loss) from operating affiliate	[2]	(32,120)	(16,273)
Income (loss) from operating affiliates	[2]	0	0
Equity in net earnings (losses) of subsidiaries	[2]	184,768	169,116
Provision (benefit) for income tax	[2]	0	0
Net income (loss)	[2]	152,648	152,843
Non-controlling interests	[2]	0	0
Net income (loss) attributable to common shareholders	[2]	152,648	152,843
Comprehensive income (loss)	[2]	(206,575)	282,271
XL-Group/XL-Ireland | Life Funds Withheld Assets
Revenues:
Net realized and unrealized gains (losses) on derivative instruments	[2]	0	0
XLIT
Revenues:
Net premiums earned		0	0
Net investment income		3,287	2,313
Total realized investment gains (losses)		(1,586)	(777)
Net realized and unrealized gains (losses) on derivative instruments		0	0
Income (loss) from investment affiliates		0	0
Fee income and other		0	0
Total revenues		1,701	1,536
Expenses:
Net losses and loss expenses incurred		0	0
Claims and policy benefits		0	0
Acquisition costs		0	0
Operating expenses		842	509
Foreign exchange (gains) losses		510	1
Interest expense		40,039	35,147
Total expenses		41,391	35,657
Income (loss) before income tax expense and income (loss) from operating affiliate		(39,690)	(34,121)
Income (loss) from operating affiliates		0	0
Equity in net earnings (losses) of subsidiaries		234,278	239,526
Provision (benefit) for income tax		0	0
Net income (loss)		194,588	205,405
Non-controlling interests		9,820	36,289
Net income (loss) attributable to common shareholders		184,768	169,116
Comprehensive income (loss)		(174,455)	298,544
XLIT | Life Funds Withheld Assets
Revenues:
Net realized and unrealized gains (losses) on derivative instruments		0	0
Other XL Subsidiaries
Revenues:
Net premiums earned		2,600,288	2,522,791
Net investment income		215,186	198,219
Total realized investment gains (losses)		(81,769)	38,063
Net realized and unrealized gains (losses) on derivative instruments		4,221	(7,069)
Income (loss) from investment affiliates		45,669	38,261
Fee income and other		6,713	13,661
Total revenues		2,813,229	2,753,825
Expenses:
Net losses and loss expenses incurred		1,622,006	1,583,456
Claims and policy benefits		10,307	7,291
Acquisition costs		463,827	435,869
Operating expenses		440,859	451,349
Foreign exchange (gains) losses		8,061	(3,513)
Interest expense		13,506	15,564
Total expenses		2,558,566	2,490,016
Income (loss) before income tax expense and income (loss) from operating affiliate		254,663	263,809
Income (loss) from operating affiliates		10,282	13,609
Equity in net earnings (losses) of subsidiaries		0	0
Provision (benefit) for income tax		31,902	13,092
Net income (loss)		233,043	264,326
Non-controlling interests		(1,235)	24,800
Net income (loss) attributable to common shareholders		234,278	239,526
Comprehensive income (loss)		(124,945)	368,954
Other XL Subsidiaries | Life Funds Withheld Assets
Revenues:
Net realized and unrealized gains (losses) on derivative instruments		$ 22,921	$ (50,101)

[1] The Company has reflected the amortization of certain fair value adjustments recorded in conjunction with the Company's acquisition of Catlin Group Ltd in 2015 ("Catlin Acquisition") within the respective segments.

[2] Includes XL-Ireland, which was the former ultimate parent and is now in liquidation proceedings. The Company expects the net assets of XL-Ireland to be distributed to XL Group upon completion of the liquidation.