Guarantor Financial Information Balance Sheet (Details) - USD ($) $ in Thousands	Jun. 30, 2016		Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
ASSETS
Total investments available for sale	$ 33,342,818		$ 33,753,898
Total investments trading	1,496,906		1,296,029
Investments in affiliates	1,968,801		1,708,899
Other investments	1,297,704		1,433,057
Investments	38,106,229		38,191,883
Cash and cash equivalents	3,316,749		3,256,236	$ 2,840,841	$ 2,521,814
Restricted cash	181,858		154,992
Investments in subsidiaries	0		0
Accrued investment income	289,911		312,667
Deferred acquisition costs and value of business acquired	1,050,653		890,568
Ceded unearned premiums	2,174,219		1,821,793
Premiums receivable	6,469,371		4,712,493
Reinsurance balances receivable	563,673		418,666
Unpaid losses and loss expenses recoverable	5,426,773		5,262,706
Receivable from investments sold	222,558		231,158
Goodwill and other intangible assets	2,217,973		2,210,266
Deferred tax asset	224,786		282,311
Amounts due from subsidiaries/parent	0		0
Other assets	953,487		937,199
Total assets	61,198,240		58,682,938
Liabilities:
Unpaid losses and loss expenses	26,020,564		25,439,744
Deposit liabilities	1,178,113		1,168,376
Future policy benefit reserves	3,798,278		4,163,500
Funds withheld on GreyCastle life retrocession arrangements	1,145,314		914,629
Unearned premiums	8,274,300		7,043,358
Notes payable and debt	2,646,324		2,644,970
Reinsurance balances payable	2,911,974		2,117,727
Payable for investments purchased	175,153		130,060
Deferred tax liability	107,778		120,651
Amounts due to subsidiaries/parent	0		0
Other liabilities (1)	1,276,510		1,285,460
Total liabilities	47,534,308		45,028,475
Shareholders' Equity:
Shareholders' equity attributable to XL Group plc	11,685,188		11,677,079
Non-controlling interest in equity of consolidated subsidiaries	1,978,744		1,977,384
Total shareholders' equity	13,663,932		13,654,463	14,205,105
Total liabilities and shareholders' equity	61,198,240		58,682,938
Consolidating Adjustments and Eliminations
ASSETS
Total investments available for sale	0		0
Total investments trading	0		0
Investments in affiliates	0		0
Other investments	0		0
Investments	0		0
Cash and cash equivalents	(174,654)	[1]	0	0	(43,293)
Restricted cash	0		0
Investments in subsidiaries	(28,379,879)		(27,485,324)
Accrued investment income	0		0
Deferred acquisition costs and value of business acquired	0		0
Ceded unearned premiums	0		0
Premiums receivable	0		0
Reinsurance balances receivable	0		0
Unpaid losses and loss expenses recoverable	0		0
Receivable from investments sold	0		0
Goodwill and other intangible assets	0		0
Deferred tax asset	0		0
Amounts due from subsidiaries/parent	(1,811,726)		(1,087,594)
Other assets	0		0
Total assets	(30,366,259)		(28,572,918)
Liabilities:
Unpaid losses and loss expenses	0		0
Deposit liabilities	0		0
Future policy benefit reserves	0		0
Funds withheld on GreyCastle life retrocession arrangements	0		0
Unearned premiums	0		0
Notes payable and debt	0		0
Reinsurance balances payable	0		0
Payable for investments purchased	0		0
Deferred tax liability	0		0
Amounts due to subsidiaries/parent	(1,811,726)		(1,087,594)
Other liabilities (1)	(174,654)	[1]	0
Total liabilities	(1,986,380)		(1,087,594)
Shareholders' Equity:
Shareholders' equity attributable to XL Group plc	(28,379,879)		(27,485,324)
Non-controlling interest in equity of consolidated subsidiaries	0		0
Total shareholders' equity	(28,379,879)		(27,485,324)
Total liabilities and shareholders' equity	(30,366,259)		(28,572,918)
XL- Ireland
ASSETS
Total investments available for sale	0		0
Total investments trading	0		0
Investments in affiliates	0		0
Other investments	0		0
Investments	0		0
Cash and cash equivalents	13,436		11,557	1,174	22,443
Restricted cash	0		0
Investments in subsidiaries	11,651,980		11,648,673
Accrued investment income	48		0
Deferred acquisition costs and value of business acquired	0		0
Ceded unearned premiums	0		0
Premiums receivable	0		0
Reinsurance balances receivable	0		0
Unpaid losses and loss expenses recoverable	0		0
Receivable from investments sold	0		0
Goodwill and other intangible assets	0		0
Deferred tax asset	0		0
Amounts due from subsidiaries/parent	26,754		33,417
Other assets	238		2,748
Total assets	11,692,456		11,696,395
Liabilities:
Unpaid losses and loss expenses	0		0
Deposit liabilities	0		0
Future policy benefit reserves	0		0
Funds withheld on GreyCastle life retrocession arrangements	0		0
Unearned premiums	0		0
Notes payable and debt	0		0
Reinsurance balances payable	0		0
Payable for investments purchased	0		0
Deferred tax liability	0		0
Amounts due to subsidiaries/parent	0		0
Other liabilities (1)	7,268		19,316
Total liabilities	7,268		19,316
Shareholders' Equity:
Shareholders' equity attributable to XL Group plc	11,685,188		11,677,079
Non-controlling interest in equity of consolidated subsidiaries	0		0
Total shareholders' equity	11,685,188		11,677,079
Total liabilities and shareholders' equity	11,692,456		11,696,395
XL-Cayman
ASSETS
Total investments available for sale	761,877		516,425
Total investments trading	0		0
Investments in affiliates	0		0
Other investments	934		877
Investments	762,811		517,302
Cash and cash equivalents	133,711	[1]	369,997	138,689	86,263
Restricted cash	0		0
Investments in subsidiaries	16,727,899		15,836,651
Accrued investment income	3,366		2,323
Deferred acquisition costs and value of business acquired	0		0
Ceded unearned premiums	0		0
Premiums receivable	0		0
Reinsurance balances receivable	0		0
Unpaid losses and loss expenses recoverable	0		0
Receivable from investments sold	0		0
Goodwill and other intangible assets	0		0
Deferred tax asset	0		0
Amounts due from subsidiaries/parent	0		0
Other assets	42,946		44,570
Total assets	17,670,733		16,770,843
Liabilities:
Unpaid losses and loss expenses	0		0
Deposit liabilities	0		0
Future policy benefit reserves	0		0
Funds withheld on GreyCastle life retrocession arrangements	0		0
Unearned premiums	0		0
Notes payable and debt	2,646,324		2,644,970
Reinsurance balances payable	0		0
Payable for investments purchased	0		0
Deferred tax liability	0		0
Amounts due to subsidiaries/parent	1,811,726		1,087,594
Other liabilities (1)	216,203	[1]	45,106
Total liabilities	4,674,253		3,777,670
Shareholders' Equity:
Shareholders' equity attributable to XL Group plc	11,651,980		11,648,673
Non-controlling interest in equity of consolidated subsidiaries	1,344,500		1,344,500
Total shareholders' equity	12,996,480		12,993,173
Total liabilities and shareholders' equity	17,670,733		16,770,843
Other XL-Ireland Subsidiaries
ASSETS
Total investments available for sale	32,580,941		33,237,473
Total investments trading	1,496,906		1,296,029
Investments in affiliates	1,968,801		1,708,899
Other investments	1,296,770		1,432,180
Investments	37,343,418		37,674,581
Cash and cash equivalents	3,344,256		2,874,682	$ 2,700,978	$ 2,456,401
Restricted cash	181,858		154,992
Investments in subsidiaries	0		0
Accrued investment income	286,497		310,344
Deferred acquisition costs and value of business acquired	1,050,653		890,568
Ceded unearned premiums	2,174,219		1,821,793
Premiums receivable	6,469,371		4,712,493
Reinsurance balances receivable	563,673		418,666
Unpaid losses and loss expenses recoverable	5,426,773		5,262,706
Receivable from investments sold	222,558		231,158
Goodwill and other intangible assets	2,217,973		2,210,266
Deferred tax asset	224,786		282,311
Amounts due from subsidiaries/parent	1,784,972		1,054,177
Other assets	910,303		889,881
Total assets	62,201,310		58,788,618
Liabilities:
Unpaid losses and loss expenses	26,020,564		25,439,744
Deposit liabilities	1,178,113		1,168,376
Future policy benefit reserves	3,798,278		4,163,500
Funds withheld on GreyCastle life retrocession arrangements	1,145,314		914,629
Unearned premiums	8,274,300		7,043,358
Notes payable and debt	0		0
Reinsurance balances payable	2,911,974		2,117,727
Payable for investments purchased	175,153		130,060
Deferred tax liability	107,778		120,651
Amounts due to subsidiaries/parent	0		0
Other liabilities (1)	1,227,693		1,221,038
Total liabilities	44,839,167		42,319,083
Shareholders' Equity:
Shareholders' equity attributable to XL Group plc	16,727,899		15,836,651
Non-controlling interest in equity of consolidated subsidiaries	634,244		632,884
Total shareholders' equity	17,362,143		16,469,535
Total liabilities and shareholders' equity	$ 62,201,310		$ 58,788,618

[1] The Company maintains a notional multi-currency cash pool with a third-party bank. At June 30, 2016, the cash pool balance of one or more entities was negative and reflected as part of Other Liabilities. Overall, the pool balance maintained by the Company is positive.