Guarantor Financial Information Cash Flows (Details) - USD ($) $ in Thousands		6 Months Ended
		Jun. 30, 2016		Jun. 30, 2015
Cash flows provided by (used in) operating activities:
Net cash provided by (used in) operating activities		$ 167,254		$ 20,504
Cash flows provided by (used in) investing activities:
Proceeds from sale of fixed maturities and short-term investments		7,449,955		6,352,126
Proceeds from redemption of fixed maturities and short-term investments		2,088,317		1,938,622
Proceeds from sale of equity securities		114,958		271,367
Purchases of fixed maturities and short term investments		(8,356,108)		(8,042,196)
Purchases of equity securities		(255,442)		(239,535)
Proceeds from sale of affiliates		153,928		86,156
Purchases of affiliates		(408,886)		(33,298)
Proceeds from sale of subsidiary				0
Proceeds from sale of affiliates		0		560,552
Return of capital from subsidiaries		0		0
Change in restricted cash		(26,866)		(135,638)
Other, net		108,095		(87,516)
Net cash provided by (used in) investing activities		798,206		(349,375)
Cash flows provided by (used in) financing activities:
Proceeds from issuance of ordinary shares and exercise of stock options		1,727		4,827
Buybacks of ordinary shares		(684,386)		(112,385)
Dividends paid on ordinary shares		(113,731)		(89,053)
Return of capital		0		0
Distributions to non-controlling interests		(65,682)		(53,456)
Contributions from non-controlling interests		1,130		4,658
Proceeds from the issuance of debt		0		980,600
Repayment of debt		(8,248)		0
Net proceeds from affiliated notional cash pooling programs	[1]	0		0
Deposit liabilities		(14,807)		(49,388)
Net cash provided by (used in) financing activities		(883,997)		685,803
Effects of exchange rate changes on foreign currency cash		(20,950)		(37,905)
Increase (decrease) in cash and cash equivalents		60,513		319,027
Cash and cash equivalents beginning of period		3,256,236		2,521,814
Cash and cash equivalents end of period		3,316,749		2,840,841
Consolidating Adjustments and Eliminations
Cash flows provided by (used in) operating activities:
Net cash provided by (used in) operating activities		(655,063)		(124,951)
Cash flows provided by (used in) investing activities:
Proceeds from sale of fixed maturities and short-term investments		(578,010)		(316,963)
Proceeds from redemption of fixed maturities and short-term investments		0		0
Proceeds from sale of equity securities		0		0
Purchases of fixed maturities and short term investments		578,010		316,963
Purchases of equity securities		0		0
Proceeds from sale of affiliates		0		0
Purchases of affiliates		0		0
Proceeds from sale of subsidiary				(2,317,699)
Proceeds from sale of affiliates				0
Return of capital from subsidiaries		(132,374)		(65,037)
Change in restricted cash		0		0
Other, net		0		0
Net cash provided by (used in) investing activities		(132,374)		(65,037)
Cash flows provided by (used in) financing activities:
Proceeds from issuance of ordinary shares and exercise of stock options		0		0
Buybacks of ordinary shares		0		0
Dividends paid on ordinary shares		655,063		124,951
Return of capital		132,374		65,037
Distributions to non-controlling interests		0		0
Contributions from non-controlling interests		0		0
Proceeds from the issuance of debt		0		0
Repayment of debt		0		0
Net proceeds from affiliated notional cash pooling programs	[1]	(174,654)		43,293
Deposit liabilities		0		0
Net cash provided by (used in) financing activities		612,783		233,281
Effects of exchange rate changes on foreign currency cash		0		0
Increase (decrease) in cash and cash equivalents		(174,654)		43,293
Cash and cash equivalents beginning of period		0		(43,293)
Cash and cash equivalents end of period		(174,654)	[2]	0
XL- Ireland
Cash flows provided by (used in) operating activities:
Net cash provided by (used in) operating activities		665,895		80,185
Cash flows provided by (used in) investing activities:
Proceeds from sale of fixed maturities and short-term investments		0		0
Proceeds from redemption of fixed maturities and short-term investments		0		0
Proceeds from sale of equity securities		0		0
Purchases of fixed maturities and short term investments		0		0
Purchases of equity securities		0		0
Proceeds from sale of affiliates		0		0
Purchases of affiliates		0		0
Proceeds from sale of subsidiary				2,317,699
Proceeds from sale of affiliates				0
Return of capital from subsidiaries		132,374		65,037
Change in restricted cash		0		0
Other, net		0		0
Net cash provided by (used in) investing activities		132,374		95,157
Cash flows provided by (used in) financing activities:
Proceeds from issuance of ordinary shares and exercise of stock options		1,727		4,827
Buybacks of ordinary shares		(684,386)		(112,385)
Dividends paid on ordinary shares		(113,731)		(89,053)
Return of capital				0
Distributions to non-controlling interests		0		0
Contributions from non-controlling interests		0		0
Proceeds from the issuance of debt		0		0
Repayment of debt		0		0
Net proceeds from affiliated notional cash pooling programs	[1]	0		0
Deposit liabilities		0		0
Net cash provided by (used in) financing activities		(796,390)		(196,611)
Effects of exchange rate changes on foreign currency cash		0		0
Increase (decrease) in cash and cash equivalents		1,879		(21,269)
Cash and cash equivalents beginning of period		11,557		22,443
Cash and cash equivalents end of period		13,436		1,174
XL-Cayman
Cash flows provided by (used in) operating activities:
Net cash provided by (used in) operating activities		656,809		1,241,157
Cash flows provided by (used in) investing activities:
Proceeds from sale of fixed maturities and short-term investments		231,600		1,407,859
Proceeds from redemption of fixed maturities and short-term investments		42,744		144,867
Proceeds from sale of equity securities		0		0
Purchases of fixed maturities and short term investments		(515,794)		(1,132,590)
Purchases of equity securities		0		0
Proceeds from sale of affiliates		0		0
Purchases of affiliates		0		0
Proceeds from sale of subsidiary				0
Proceeds from sale of affiliates				0
Return of capital from subsidiaries		0		0
Change in restricted cash		0		0
Other, net		0		0
Net cash provided by (used in) investing activities		(241,450)		(1,897,563)
Cash flows provided by (used in) financing activities:
Proceeds from issuance of ordinary shares and exercise of stock options		0		0
Buybacks of ordinary shares		0		0
Dividends paid on ordinary shares		(655,063)		(124,951)
Return of capital		(132,374)		(65,037)
Distributions to non-controlling interests		(38,862)		(38,487)
Contributions from non-controlling interests		0		0
Proceeds from the issuance of debt		0		980,600
Repayment of debt		0		0
Net proceeds from affiliated notional cash pooling programs	[1]	174,654		(43,293)
Deposit liabilities		0		0
Net cash provided by (used in) financing activities		(651,645)		708,832
Effects of exchange rate changes on foreign currency cash		0		0
Increase (decrease) in cash and cash equivalents		(236,286)		52,426
Cash and cash equivalents beginning of period		369,997		86,263
Cash and cash equivalents end of period		133,711	[2]	138,689
Other XL-Ireland Subsidiaries
Cash flows provided by (used in) operating activities:
Net cash provided by (used in) operating activities		(500,387)		(1,175,887)
Cash flows provided by (used in) investing activities:
Proceeds from sale of fixed maturities and short-term investments		7,796,365		5,261,230
Proceeds from redemption of fixed maturities and short-term investments		2,045,573		1,793,755
Proceeds from sale of equity securities		114,958		271,367
Purchases of fixed maturities and short term investments		(8,418,324)		(7,226,569)
Purchases of equity securities		(255,442)		(239,535)
Proceeds from sale of affiliates		153,928		86,156
Purchases of affiliates		(408,886)		(33,298)
Proceeds from sale of subsidiary				0
Proceeds from sale of affiliates				560,552
Return of capital from subsidiaries		0		0
Change in restricted cash		(26,866)		(135,638)
Other, net		108,095		(87,516)
Net cash provided by (used in) investing activities		1,039,656		1,518,068
Cash flows provided by (used in) financing activities:
Proceeds from issuance of ordinary shares and exercise of stock options		0		0
Buybacks of ordinary shares		0		0
Dividends paid on ordinary shares		0		0
Return of capital		0		0
Distributions to non-controlling interests		(26,820)		(14,969)
Contributions from non-controlling interests		1,130		4,658
Proceeds from the issuance of debt		0		0
Repayment of debt		(8,248)		0
Net proceeds from affiliated notional cash pooling programs	[1]	0		0
Deposit liabilities		(14,807)		(49,388)
Net cash provided by (used in) financing activities		(48,745)		(59,699)
Effects of exchange rate changes on foreign currency cash		(20,950)		(37,905)
Increase (decrease) in cash and cash equivalents		469,574		244,577
Cash and cash equivalents beginning of period		2,874,682		2,456,401
Cash and cash equivalents end of period		3,344,256		2,700,978
Allied International Holdings, Inc.
Cash flows provided by (used in) investing activities:
Payments for acquisitions of businesses, net of cash acquired		(69,745)		0
Allied International Holdings, Inc. | Consolidating Adjustments and Eliminations
Cash flows provided by (used in) investing activities:
Payments for acquisitions of businesses, net of cash acquired		0
Allied International Holdings, Inc. | XL- Ireland
Cash flows provided by (used in) investing activities:
Payments for acquisitions of businesses, net of cash acquired		0
Allied International Holdings, Inc. | XL-Cayman
Cash flows provided by (used in) investing activities:
Payments for acquisitions of businesses, net of cash acquired		0
Allied International Holdings, Inc. | Other XL-Ireland Subsidiaries
Cash flows provided by (used in) investing activities:
Payments for acquisitions of businesses, net of cash acquired		(69,745)
Catlin Group Limited
Cash flows provided by (used in) investing activities:
Payments for acquisitions of businesses, net of cash acquired		$ 0		(1,020,015)
Catlin Group Limited | Consolidating Adjustments and Eliminations
Cash flows provided by (used in) investing activities:
Payments for acquisitions of businesses, net of cash acquired				2,317,699
Catlin Group Limited | XL- Ireland
Cash flows provided by (used in) investing activities:
Payments for acquisitions of businesses, net of cash acquired				(2,287,579)
Catlin Group Limited | XL-Cayman
Cash flows provided by (used in) investing activities:
Payments for acquisitions of businesses, net of cash acquired				(2,317,699)
Catlin Group Limited | Other XL-Ireland Subsidiaries
Cash flows provided by (used in) investing activities:
Payments for acquisitions of businesses, net of cash acquired				$ 1,267,564

[1] Net proceeds from affiliated notional cash pooling arrangements reflect the net impact of bank transfers to settle overdraft positions within the Company's multi-currency cash pool.

[2] 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.