Guarantor Financial Information Cash Flows (Details) - USD ($) $ in Thousands		6 Months Ended
		Jun. 30, 2017		Jun. 30, 2016
Cash flows provided by (used in) operating activities:
Net cash provided by (used in) operating activities		$ (129,246)		$ 195,201
Cash flows provided by (used in) investing activities:
Proceeds from sale of fixed maturities and short-term investments		6,387,610		7,449,955
Proceeds from redemption of fixed maturities and short-term investments		2,084,182		2,088,317
Proceeds from sale of equity securities		228,914		114,958
Purchases of fixed maturities and short term investments		(8,719,024)		(8,356,108)
Purchases of equity securities		(277,329)		(255,442)
Proceeds from sale of affiliates		236,861		153,928
Purchases of affiliates		(51,891)		(408,886)
Purchase of subsidiaries, net of cash acquired		0		(69,745)
Return of capital from subsidiaries		0		0
Change in restricted cash		(27,726)		(26,866)
Other, net		5,127		108,095
Net cash provided by (used in) investing activities		(133,276)		798,206
Cash flows provided by (used in) financing activities:
Proceeds from issuance of ordinary shares and exercise of stock options		42,630		1,727
Buybacks of common shares		(450,629)		(684,386)
Employee withholding on share-based compensation		(23,957)		(27,947)
Dividends paid on common shares		(115,589)		(113,731)
Return of Capital To Parent Financing Activities		0		0
Distributions to non-controlling interests		(73,708)		(65,682)
Contributions from non-controlling interests		25		1,130
Proceeds from Issuance of Long-term Debt		558,311		0
Repayment of debt		0		8,248
Net proceeds from affiliated notional cash pooling programs	[1]			0
Deposit liabilities		(11,150)		(14,807)
Net cash provided by (used in) financing activities		(74,067)		(911,944)
Effects of exchange rate changes on foreign currency cash		43,423		(20,950)
Increase (decrease) in cash and cash equivalents		(293,166)		60,513
Cash and cash equivalents beginning of period		3,426,988		3,256,236
Cash and cash equivalents end of period		3,133,822		3,316,749
Consolidating Adjustments and Eliminations
Cash flows provided by (used in) operating activities:
Net cash provided by (used in) operating activities		(695,987)		(655,063)
Cash flows provided by (used in) investing activities:
Proceeds from sale of fixed maturities and short-term investments		0		(578,010)
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		578,010
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
Return of capital from subsidiaries		(237,013)		(132,374)
Change in restricted cash		0		0
Other, net		0		0
Net cash provided by (used in) investing activities		(237,013)		(132,374)
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		695,987		655,063
Return of Capital To Parent Financing Activities		237,013		132,374
Distributions to non-controlling interests		0		0
Contributions from non-controlling interests		0		0
Proceeds from Issuance of Long-term Debt		0
Repayment of debt				0
Net proceeds from affiliated notional cash pooling programs	[1]			(174,654)
Deposit liabilities		0		0
Net cash provided by (used in) financing activities		933,000		612,783
Effects of exchange rate changes on foreign currency cash		0		0
Increase (decrease) in cash and cash equivalents		0		(174,654)
Cash and cash equivalents beginning of period		0		0
Cash and cash equivalents end of period		0		(174,654)
XL- Bermuda/Ireland
Cash flows provided by (used in) operating activities:
Net cash provided by (used in) operating activities		286,697	[2]	665,895
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
Return of capital from subsidiaries		237,013	[2]	132,374
Change in restricted cash		0	[2]	0
Other, net		0	[2]	0
Net cash provided by (used in) investing activities		237,013	[2]	132,374
Cash flows provided by (used in) financing activities:
Proceeds from issuance of ordinary shares and exercise of stock options		42,630	[2]	1,727
Buybacks of common shares		(450,629)	[2]	(684,386)
Employee withholding on share-based compensation		0	[2]	0
Dividends paid on common shares		(115,589)	[2]	(113,731)
Return of Capital To Parent Financing Activities		0	[2]	0
Distributions to non-controlling interests		0	[2]	0
Contributions from non-controlling interests		0	[2]	0
Proceeds from Issuance of Long-term Debt		0
Repayment of debt				0
Net proceeds from affiliated notional cash pooling programs	[1]			0
Deposit liabilities		0	[2]	0
Net cash provided by (used in) financing activities		(523,588)	[2]	(796,390)
Effects of exchange rate changes on foreign currency cash		0	[2]	0
Increase (decrease) in cash and cash equivalents		122	[2]	1,879
Cash and cash equivalents beginning of period		1,022	[2]	11,557
Cash and cash equivalents end of period		1,144	[2]	13,436
XLIT
Cash flows provided by (used in) operating activities:
Net cash provided by (used in) operating activities		332,788		656,809
Cash flows provided by (used in) investing activities:
Proceeds from sale of fixed maturities and short-term investments		81,662		231,600
Proceeds from redemption of fixed maturities and short-term investments		82,392		42,744
Proceeds from sale of equity securities		677		0
Purchases of fixed maturities and short term investments		(143,851)		(515,794)
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
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		20,880		(241,450)
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		(295,987)		(655,063)
Return of Capital To Parent Financing Activities		(237,013)		(132,374)
Distributions to non-controlling interests		(39,867)		(38,862)
Contributions from non-controlling interests		0		0
Proceeds from Issuance of Long-term Debt		558,311
Repayment of debt				0
Net proceeds from affiliated notional cash pooling programs	[1]			174,654
Deposit liabilities		0		0
Net cash provided by (used in) financing activities		(14,556)		(651,645)
Effects of exchange rate changes on foreign currency cash		0		0
Increase (decrease) in cash and cash equivalents		339,112		(236,286)
Cash and cash equivalents beginning of period		84,286		369,997
Cash and cash equivalents end of period		423,398		133,711
Other XL Subsidiaries
Cash flows provided by (used in) operating activities:
Net cash provided by (used in) operating activities		(52,744)		(472,440)
Cash flows provided by (used in) investing activities:
Proceeds from sale of fixed maturities and short-term investments		6,305,948		7,796,365
Proceeds from redemption of fixed maturities and short-term investments		2,001,790		2,045,573
Proceeds from sale of equity securities		228,237		114,958
Purchases of fixed maturities and short term investments		(8,575,173)		(8,418,324)
Purchases of equity securities		(277,329)		(255,442)
Proceeds from sale of affiliates		236,861		153,928
Purchases of affiliates		(51,891)		(408,886)
Purchase of subsidiaries, net of cash acquired				(69,745)
Return of capital from subsidiaries		0		0
Change in restricted cash		(27,726)		(26,866)
Other, net		5,127		108,095
Net cash provided by (used in) investing activities		(154,156)		1,039,656
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		(23,957)		(27,947)
Dividends paid on common shares		(400,000)		0
Return of Capital To Parent Financing Activities		0		0
Distributions to non-controlling interests		(33,841)		(26,820)
Contributions from non-controlling interests		25		1,130
Proceeds from Issuance of Long-term Debt		0
Repayment of debt				8,248
Net proceeds from affiliated notional cash pooling programs	[1]			0
Deposit liabilities		(11,150)		(14,807)
Net cash provided by (used in) financing activities		(468,923)		(76,692)
Effects of exchange rate changes on foreign currency cash		43,423		(20,950)
Increase (decrease) in cash and cash equivalents		(632,400)		469,574
Cash and cash equivalents beginning of period		3,341,680		2,874,682
Cash and cash equivalents end of period		$ 2,709,280		$ 3,344,256

[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, "Significant Accounting Policies." The Company expects the net assets of XL-Ireland to ultimately be distributed to XL Group upon completion of the liquidation.