Guarantor Financial Information Cash Flows (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2017		Mar. 31, 2016
Cash flows provided by (used in) operating activities:
Net cash provided by (used in) operating activities		$ (47,497)		$ (144,039)
Cash flows provided by (used in) investing activities:
Proceeds from sale of fixed maturities and short-term investments		2,492,005		3,772,077
Proceeds from redemption of fixed maturities and short-term investments		1,228,356		949,221
Proceeds from sale of equity securities		46,379		62,895
Purchases of fixed maturities and short term investments		(3,633,007)		(4,325,679)
Purchases of equity securities		(47,967)		(55,411)
Proceeds from sale of affiliates		168,237		41,538
Purchases of affiliates		(35,926)		(247,049)
Purchase of subsidiaries, net of cash acquired		0		(69,745)
Proceeds from sale of subsidiaries, net of cash sold		0
Return of capital from subsidiaries		0
Change in restricted cash		(7,019)		(6,027)
Other, net		23,429		82,141
Net cash provided by (used in) investing activities		234,487		203,961
Cash flows provided by (used in) financing activities:
Proceeds from issuance of ordinary shares and exercise of stock options		23,296		491
Buybacks of common shares		(200,488)		(355,901)
Employee withholding on share-based compensation		(22,871)		(27,074)
Dividends paid on common shares		(58,392)		(57,861)
Distributions to non-controlling interests		(25,400)		(27,857)
Contributions from non-controlling interests		26		883
Deposit liabilities		(7,771)		(8,546)
Net cash provided by (used in) financing activities		(291,600)		(475,865)
Effects of exchange rate changes on foreign currency cash		30,273		(19,396)
Increase (decrease) in cash and cash equivalents		(74,337)		(435,339)
Cash and cash equivalents beginning of period		3,426,988		3,256,236
Cash and cash equivalents end of period		3,352,651		2,820,897
Consolidating Adjustments and Eliminations
Cash flows provided by (used in) operating activities:
Net cash provided by (used in) operating activities		(400,000)		0
Cash flows provided by (used in) investing activities:
Proceeds from sale of fixed maturities and short-term investments		0		(176,454)
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		176,454
Purchases of equity securities		0		0
Proceeds from sale of affiliates		0		0
Purchases of affiliates		0		0
Purchase of subsidiaries, net of cash acquired		0		0
Proceeds from sale of subsidiaries, net of cash sold		0
Return of capital from subsidiaries		0
Change in restricted cash		0		0
Other, net		0		0
Net cash provided by (used in) investing activities		0		0
Cash flows provided by (used in) financing activities:
Proceeds from issuance of ordinary shares and exercise of stock options		0		0
Buybacks of common shares		0		0
Employee withholding on share-based compensation		0		0
Dividends paid on common shares		400,000		0
Distributions to non-controlling interests		0		0
Contributions from non-controlling interests		0		0
Deposit liabilities		0		0
Net cash provided by (used in) financing activities		400,000		0
Effects of exchange rate changes on foreign currency cash		0		0
Increase (decrease) in cash and cash equivalents		0		0
Cash and cash equivalents beginning of period		0		0
Cash and cash equivalents end of period		0		0
XL- Bermuda/Ireland
Cash flows provided by (used in) operating activities:
Net cash provided by (used in) operating activities		235,642	[1]	410,395
Cash flows provided by (used in) investing activities:
Proceeds from sale of fixed maturities and short-term investments		0	[1]	0
Proceeds from redemption of fixed maturities and short-term investments		0	[1]	0
Proceeds from sale of equity securities		0	[1]	0
Purchases of fixed maturities and short term investments		0	[1]	0
Purchases of equity securities		0	[1]	0
Proceeds from sale of affiliates		0	[1]	0
Purchases of affiliates		0	[1]	0
Purchase of subsidiaries, net of cash acquired		0	[1]	0
Proceeds from sale of subsidiaries, net of cash sold	[1]	0
Return of capital from subsidiaries	[1]	0
Change in restricted cash		0	[1]	0
Other, net		0	[1]	0
Net cash provided by (used in) investing activities		0	[1]	0
Cash flows provided by (used in) financing activities:
Proceeds from issuance of ordinary shares and exercise of stock options		23,296	[1]	491
Buybacks of common shares		(200,488)	[1]	(355,901)
Employee withholding on share-based compensation		0	[1]	0
Dividends paid on common shares		(58,392)	[1]	(57,861)
Distributions to non-controlling interests		0	[1]	0
Contributions from non-controlling interests		0	[1]	0
Deposit liabilities		0	[1]	0
Net cash provided by (used in) financing activities		(235,584)	[1]	(413,271)
Effects of exchange rate changes on foreign currency cash		0	[1]	0
Increase (decrease) in cash and cash equivalents		58	[1]	(2,876)
Cash and cash equivalents beginning of period		1,022	[1]	11,557
Cash and cash equivalents end of period		1,080	[1]	8,681
XL-Cayman
Cash flows provided by (used in) operating activities:
Net cash provided by (used in) operating activities		118,694		(48,205)
Cash flows provided by (used in) investing activities:
Proceeds from sale of fixed maturities and short-term investments		547		132,687
Proceeds from redemption of fixed maturities and short-term investments		44,453		26,181
Proceeds from sale of equity securities		677		0
Purchases of fixed maturities and short term investments		(3,098)		(190,119)
Purchases of equity securities		0		0
Proceeds from sale of affiliates		0		0
Purchases of affiliates		0		0
Purchase of subsidiaries, net of cash acquired		0		0
Proceeds from sale of subsidiaries, net of cash sold		0
Return of capital from subsidiaries		0
Change in restricted cash		0		0
Other, net		0		0
Net cash provided by (used in) investing activities		42,579		(31,251)
Cash flows provided by (used in) financing activities:
Proceeds from issuance of ordinary shares and exercise of stock options		0		0
Buybacks of common shares		0		0
Employee withholding on share-based compensation		0		0
Dividends paid on common shares		0		0
Distributions to non-controlling interests		(3,701)		(3,077)
Contributions from non-controlling interests		0		0
Deposit liabilities		0		0
Net cash provided by (used in) financing activities		(3,701)		(3,077)
Effects of exchange rate changes on foreign currency cash		0		0
Increase (decrease) in cash and cash equivalents		157,572		(82,533)
Cash and cash equivalents beginning of period		84,286		369,997
Cash and cash equivalents end of period		241,858		287,464
Other XL Subsidiaries
Cash flows provided by (used in) operating activities:
Net cash provided by (used in) operating activities		(1,833)		(506,229)
Cash flows provided by (used in) investing activities:
Proceeds from sale of fixed maturities and short-term investments		2,491,458		3,815,844
Proceeds from redemption of fixed maturities and short-term investments		1,183,903		923,040
Proceeds from sale of equity securities		45,702		62,895
Purchases of fixed maturities and short term investments		(3,629,909)		(4,312,014)
Purchases of equity securities		(47,967)		(55,411)
Proceeds from sale of affiliates		168,237		41,538
Purchases of affiliates		(35,926)		(247,049)
Purchase of subsidiaries, net of cash acquired		0		(69,745)
Proceeds from sale of subsidiaries, net of cash sold		0
Return of capital from subsidiaries		0
Change in restricted cash		(7,019)		(6,027)
Other, net		23,429		82,141
Net cash provided by (used in) investing activities		191,908		235,212
Cash flows provided by (used in) financing activities:
Proceeds from issuance of ordinary shares and exercise of stock options		0		0
Buybacks of common shares		0		0
Employee withholding on share-based compensation		(22,871)		(27,074)
Dividends paid on common shares		(400,000)		0
Distributions to non-controlling interests		(21,699)		(24,780)
Contributions from non-controlling interests		26		883
Deposit liabilities		(7,771)		(8,546)
Net cash provided by (used in) financing activities		(452,315)		(59,517)
Effects of exchange rate changes on foreign currency cash		30,273		(19,396)
Increase (decrease) in cash and cash equivalents		(231,967)		(349,930)
Cash and cash equivalents beginning of period		3,341,680		2,874,682
Cash and cash equivalents end of period		$ 3,109,713		$ 2,524,752

[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.