Guarantor Financial Information Cash Flows (Details) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2016		Sep. 30, 2015
Cash flows provided by (used in) operating activities:
Net cash provided by (used in) operating activities		$ 649,611		$ 509,500
Cash flows provided by (used in) investing activities:
Proceeds from sale of fixed maturities and short-term investments		9,581,243		10,568,708
Proceeds from redemption of fixed maturities and short-term investments		3,010,158		2,787,870
Proceeds from sale of equity securities		411,330		443,941
Purchases of fixed maturities and short term investments		(11,557,045)		(12,720,937)
Purchases of equity securities		(611,086)		(436,622)
Proceeds from sale of affiliates		325,050		724,382
Purchases of affiliates		(556,548)		(94,745)
Purchase of subsidiaries, net of cash acquired		(92,893)		(1,020,015)
Proceeds from sale of subsidiaries, net of cash sold		19,144		0
Return of capital from subsidiaries		0		0
Change in restricted cash		4,874		(147,810)
Other, net		193,392		(138,168)
Net cash provided by (used in) investing activities		727,619		(33,396)
Cash flows provided by (used in) financing activities:
Proceeds from issuance of ordinary shares and exercise of stock options		5,735		7,904
Buybacks of ordinary shares		(906,137)		(292,269)
Dividends paid on ordinary shares		(169,346)		(149,030)
Return of capital		0		0
Distributions to non-controlling interests		(93,470)		(80,641)
Contributions from non-controlling interests		6,394		10,292
Proceeds from the issuance of debt		0		980,600
Repayment of debt		(8,248)		0
Net proceeds from affiliated notional cash pooling programs				0
Deposit liabilities		(63,488)		(79,944)
Net cash provided by (used in) financing activities		(1,228,560)		396,912
Effects of exchange rate changes on foreign currency cash		(11,629)		(54,760)
Increase (decrease) in cash and cash equivalents		137,041		818,256
Cash and cash equivalents beginning of period		3,256,236		2,521,814
Cash and cash equivalents end of period		3,393,277		3,340,070
Consolidating Adjustments and Eliminations
Cash flows provided by (used in) operating activities:
Net cash provided by (used in) operating activities		(2,315,848)		(273,048)
Cash flows provided by (used in) investing activities:
Proceeds from sale of fixed maturities and short-term investments		(583,466)		(359,897)
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		583,466		359,897
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		2,317,699
Proceeds from sale of subsidiaries, net of cash sold		0		(2,317,699)
Return of capital from subsidiaries		(614,661)		(65,037)
Change in restricted cash		0		0
Other, net		0		0
Net cash provided by (used in) investing activities		(614,661)		(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		2,315,848		273,048
Return of capital		614,661		65,037
Distributions to non-controlling interests		0		0
Contributions from non-controlling interests		0		0
Proceeds from the issuance of debt				0
Repayment of debt		0
Net proceeds from affiliated notional cash pooling programs	[1]			43,293
Deposit liabilities		0		0
Net cash provided by (used in) financing activities		2,930,509		381,378
Effects of exchange rate changes on foreign currency cash		0		0
Increase (decrease) in cash and cash equivalents		0		43,293
Cash and cash equivalents beginning of period		0		(43,293)
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		921,608	[2]	319,352
Cash flows provided by (used in) investing activities:
Proceeds from sale of fixed maturities and short-term investments		0	[2]	0
Proceeds from redemption of fixed maturities and short-term investments		0	[2]	0
Proceeds from sale of equity securities		0	[2]	0
Purchases of fixed maturities and short term investments		0	[2]	0
Purchases of equity securities		0	[2]	0
Proceeds from sale of affiliates		0	[2]	0
Purchases of affiliates		0	[2]	0
Purchase of subsidiaries, net of cash acquired		0		(2,287,579)
Proceeds from sale of subsidiaries, net of cash sold		0	[2]	2,317,699
Return of capital from subsidiaries		149,458	[2]	65,037
Change in restricted cash		0	[2]	0
Other, net		0	[2]	0
Net cash provided by (used in) investing activities		149,458	[2]	95,157
Cash flows provided by (used in) financing activities:
Proceeds from issuance of ordinary shares and exercise of stock options		5,735	[2]	7,904
Buybacks of ordinary shares		(906,137)	[2]	(292,269)
Dividends paid on ordinary shares		(169,346)	[2]	(149,030)
Return of capital		0	[2]	0
Distributions to non-controlling interests		0	[2]	0
Contributions from non-controlling interests		0	[2]	0
Proceeds from the issuance of debt				0
Repayment of debt	[2]	0
Net proceeds from affiliated notional cash pooling programs	[1]			0
Deposit liabilities		0	[2]	0
Net cash provided by (used in) financing activities		(1,069,748)	[2]	(433,395)
Effects of exchange rate changes on foreign currency cash		0	[2]	0
Increase (decrease) in cash and cash equivalents		1,318	[2]	(18,886)
Cash and cash equivalents beginning of period		11,557	[2]	22,443
Cash and cash equivalents end of period		12,875	[2]	3,557
XL-Cayman
Cash flows provided by (used in) operating activities:
Net cash provided by (used in) operating activities		230,877		1,422,263
Cash flows provided by (used in) investing activities:
Proceeds from sale of fixed maturities and short-term investments		300,452		1,461,428
Proceeds from redemption of fixed maturities and short-term investments		65,881		161,989
Proceeds from sale of equity securities		0		0
Purchases of fixed maturities and short term investments		(526,206)		(1,174,294)
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		(2,317,699)
Proceeds from sale of subsidiaries, net of cash sold		0		0
Return of capital from subsidiaries		465,203		0
Change in restricted cash		0		0
Other, net		0		0
Net cash provided by (used in) investing activities		305,330		(1,868,576)
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		(700,063)		(273,048)
Return of capital		(149,458)		(65,037)
Distributions to non-controlling interests		(42,188)		(41,490)
Contributions from non-controlling interests		0		0
Proceeds from the issuance of debt				980,600
Repayment of debt		0
Net proceeds from affiliated notional cash pooling programs	[1]			(43,293)
Deposit liabilities		0		0
Net cash provided by (used in) financing activities		(891,709)		557,732
Effects of exchange rate changes on foreign currency cash		0		0
Increase (decrease) in cash and cash equivalents		(355,502)		111,419
Cash and cash equivalents beginning of period		369,997		86,263
Cash and cash equivalents end of period		14,495		197,682
Other XL Subsidiaries
Cash flows provided by (used in) operating activities:
Net cash provided by (used in) operating activities		1,812,974		(959,067)
Cash flows provided by (used in) investing activities:
Proceeds from sale of fixed maturities and short-term investments		9,864,257		9,467,177
Proceeds from redemption of fixed maturities and short-term investments		2,944,277		2,625,881
Proceeds from sale of equity securities		411,330		443,941
Purchases of fixed maturities and short term investments		(11,614,305)		(11,906,540)
Purchases of equity securities		(611,086)		(436,622)
Proceeds from sale of affiliates		325,050		724,382
Purchases of affiliates		(556,548)		(94,745)
Purchase of subsidiaries, net of cash acquired		(92,893)		1,267,564
Proceeds from sale of subsidiaries, net of cash sold		19,144		0
Return of capital from subsidiaries		0		0
Change in restricted cash		4,874		(147,810)
Other, net		193,392		(138,168)
Net cash provided by (used in) investing activities		887,492		1,805,060
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		(1,615,785)		0
Return of capital		(465,203)		0
Distributions to non-controlling interests		(51,282)		(39,151)
Contributions from non-controlling interests		6,394		10,292
Proceeds from the issuance of debt				0
Repayment of debt		(8,248)
Net proceeds from affiliated notional cash pooling programs	[1]			0
Deposit liabilities		(63,488)		(79,944)
Net cash provided by (used in) financing activities		(2,197,612)		(108,803)
Effects of exchange rate changes on foreign currency cash		(11,629)		(54,760)
Increase (decrease) in cash and cash equivalents		491,225		682,430
Cash and cash equivalents beginning of period		2,874,682		2,456,401
Cash and cash equivalents end of period		$ 3,365,907		$ 3,138,831

[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] 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, "Basis of Preparation and Consolidation." The Company expects the net assets of XL-Ireland to ultimately be distributed to XL-Bermuda upon completion of the liquidation.