Guarantor Financial Information Balance Sheet (Details) - USD ($) $ in Thousands		Mar. 31, 2017		Dec. 31, 2016		Mar. 31, 2016	Dec. 31, 2015
ASSETS
Total investments available for sale		$ 32,006,452		$ 31,919,126
Total investments trading		1,700,862		1,626,577
Investments in affiliates		2,172,611		2,177,645
Other investments		1,150,492		1,164,564
Investments		37,030,417		36,887,912
Cash and cash equivalents		3,352,651		3,426,988		$ 2,820,897	$ 3,256,236
Restricted cash		160,523		153,504
Investments in subsidiaries		0		0
Accrued investment income		262,237		284,366
Deferred acquisition costs and value of business acquired		1,161,159		946,721
Ceded unearned premiums		2,501,294		1,687,864
Premiums receivable		6,746,116		5,522,976
Reinsurance balances receivable		641,720		577,479
Unpaid losses and loss expenses recoverable		5,685,623		5,491,297
Receivable from investments sold		95,344		128,411
Goodwill and other intangible assets		2,208,612		2,203,653
Deferred tax asset		302,301		310,542
Amounts due from subsidiaries/parent		0		0
Other assets		876,622		812,389
Total assets		61,024,619		58,434,102
Liabilities:
Unpaid losses and loss expenses		26,445,124		25,939,571		25,913,484	25,439,744
Deposit liabilities		1,121,194		1,116,233
Future policy benefit reserves		3,520,069		3,506,047
Funds withheld on GreyCastle life retrocession arrangements		954,327		998,968
Unearned premiums		8,581,973		7,293,028
Notes payable and debt		2,648,353		2,647,677
Reinsurance balances payable		3,325,748		2,451,717
Payable for investments purchased		211,880		226,009
Deferred tax liability		89,862		77,271
Amounts due to subsidiaries/parent		0		0
Other liabilities		1,125,463		1,216,902
Total liabilities		48,023,993		45,473,423
Shareholders' Equity:
Shareholders' equity attributable to XL Group Ltd		10,974,884		10,938,512
Non-controlling interest in equity of consolidated subsidiaries		2,025,742		2,022,167
Total shareholders' equity		13,000,626		12,960,679		13,667,718
Total liabilities and shareholders' equity		61,024,619		58,434,102
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		0		0		0	0
Restricted cash		0		0
Investments in subsidiaries		(25,402,002)		(25,135,893)
Accrued investment income		(74)		(55)
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		(388,348)		(115,742)
Other assets		0		0
Total assets		(25,790,424)		(25,251,690)
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		(388,348)		(115,742)
Other liabilities		0		0
Total liabilities		(388,348)		(115,742)
Shareholders' Equity:
Shareholders' equity attributable to XL Group Ltd		(25,396,502)		(25,135,893)
Non-controlling interest in equity of consolidated subsidiaries		(5,574)		(55)
Total shareholders' equity		(25,402,076)		(25,135,948)
Total liabilities and shareholders' equity		(25,790,424)		(25,251,690)
XL- Bermuda/Ireland
ASSETS
Total investments available for sale	[1]	0		0
Total investments trading	[1]	0		0
Investments in affiliates	[1]	0		0
Other investments	[1]	0		0
Investments	[1]	0		0
Cash and cash equivalents		1,080	[1]	1,022	[1]	8,681	11,557
Restricted cash	[1]	0		0
Investments in subsidiaries	[1]	11,195,738	[2]	10,897,195
Accrued investment income	[1]	74		55
Deferred acquisition costs and value of business acquired	[1]	0		0
Ceded unearned premiums	[1]	0		0
Premiums receivable	[1]	0		0
Reinsurance balances receivable	[1]	0		0
Unpaid losses and loss expenses recoverable	[1]	0		0
Receivable from investments sold	[1]	0		0
Goodwill and other intangible assets	[1]	0		0
Deferred tax asset	[1]	0		0
Amounts due from subsidiaries/parent	[1]	0		42,780
Other assets	[1]	16,134		15,188
Total assets	[1]	11,213,026		10,956,240
Liabilities:
Unpaid losses and loss expenses	[1]	0		0
Deposit liabilities	[1]	0		0
Future policy benefit reserves	[1]	0		0
Funds withheld on GreyCastle life retrocession arrangements	[1]	0		0
Unearned premiums	[1]	0		0
Notes payable and debt	[1]	0		0
Reinsurance balances payable	[1]	0		0
Payable for investments purchased	[1]	0		0
Deferred tax liability	[1]	0		0
Amounts due to subsidiaries/parent	[1]	213,477		0
Other liabilities	[1]	24,665		17,728
Total liabilities	[1]	238,142		17,728
Shareholders' Equity:
Shareholders' equity attributable to XL Group Ltd	[1]	10,974,884		10,938,512
Non-controlling interest in equity of consolidated subsidiaries	[1]	0		0
Total shareholders' equity	[1]	10,974,884		10,938,512
Total liabilities and shareholders' equity	[1]	11,213,026		10,956,240
XL-Cayman
ASSETS
Total investments available for sale		594,823		638,236
Total investments trading		0		0
Investments in affiliates		0		0
Other investments		0		9
Investments		594,823		638,245
Cash and cash equivalents		241,858		84,286		287,464	369,997
Restricted cash		0		0
Investments in subsidiaries		14,206,264		14,238,698
Accrued investment income		2,985		2,981
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		174,871		0
Other assets		35,529		40,108
Total assets		15,256,330		15,004,318
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
Notes payable and debt		2,648,353		2,647,677
Reinsurance balances payable		0		0
Payable for investments purchased		0		0
Deferred tax liability		0		0
Amounts due to subsidiaries/parent		0		72,962
Other liabilities		67,739		41,984
Total liabilities		2,716,092		2,762,623
Shareholders' Equity:
Shareholders' equity attributable to XL Group Ltd		11,190,238		10,897,195
Non-controlling interest in equity of consolidated subsidiaries		1,350,000		1,344,500
Total shareholders' equity		12,540,238		12,241,695
Total liabilities and shareholders' equity		15,256,330		15,004,318
Other XL Subsidiaries
ASSETS
Total investments available for sale		31,411,629		31,280,890
Total investments trading		1,700,862		1,626,577
Investments in affiliates		2,172,611		2,177,645
Other investments		1,150,492		1,164,555
Investments		36,435,594		36,249,667
Cash and cash equivalents		3,109,713		3,341,680		$ 2,524,752	$ 2,874,682
Restricted cash		160,523		153,504
Investments in subsidiaries		0		0
Accrued investment income		259,252		281,385
Deferred acquisition costs and value of business acquired		1,161,159		946,721
Ceded unearned premiums		2,501,294		1,687,864
Premiums receivable		6,746,116		5,522,976
Reinsurance balances receivable		641,720		577,479
Unpaid losses and loss expenses recoverable		5,685,623		5,491,297
Receivable from investments sold		95,344		128,411
Goodwill and other intangible assets		2,208,612		2,203,653
Deferred tax asset		302,301		310,542
Amounts due from subsidiaries/parent		213,477		72,962
Other assets		824,959		757,093
Total assets		60,345,687		57,725,234
Liabilities:
Unpaid losses and loss expenses		26,445,124		25,939,571
Deposit liabilities		1,121,194		1,116,233
Future policy benefit reserves		3,520,069		3,506,047
Funds withheld on GreyCastle life retrocession arrangements		954,327		998,968
Unearned premiums		8,581,973		7,293,028
Notes payable and debt		0		0
Reinsurance balances payable		3,325,748		2,451,717
Payable for investments purchased		211,880		226,009
Deferred tax liability		89,862		77,271
Amounts due to subsidiaries/parent		174,871		42,780
Other liabilities		1,033,059		1,157,190
Total liabilities		45,458,107		42,808,814
Shareholders' Equity:
Shareholders' equity attributable to XL Group Ltd		14,206,264		14,238,698
Non-controlling interest in equity of consolidated subsidiaries		681,316		677,722
Total shareholders' equity		14,887,580		14,916,420
Total liabilities and shareholders' equity		$ 60,345,687		$ 57,725,234

[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.

[2] XL-Bermuda balance includes investment in $5.5 million of XL-Cayman Series D Preference Ordinary Shares and XL-Cayman Series E Non-Cumulative Preference Ordinary Shares.