Statutory Financial Data (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
XL-Ireland
Statutory Accounting Practices [Line Items]
Cash and investments, net of liabilities associated with cash sweeping arrangements	$ 22,400,000		$ 12,700,000
XL-Cayman
Statutory Accounting Practices [Line Items]
Cash and investments, net of liabilities associated with cash sweeping arrangements	900,000,000		1,600,000,000
Bermuda
Statutory Accounting Practices [Line Items]
Required statutory capital and surplus	6,194,832,000	[1]	6,583,273,000	[1]
Actual statutory capital and surplus	10,309,895,000	[1],[2]	10,168,744,000	[1],[2]
Statutory net income (loss)	361,033,000		1,241,878,000		857,832,000
BSCR level for principal operating subsidiaries	100.00%
Maximum permitted dividends as a percentage of prior year statutory capital and surplus	25.00%
Maximum permitted dividends as a percentage of statutory capital	15.00%
Maximum dividend permitted without affidavit	1,400,000,000		1,400,000,000
United States
Statutory Accounting Practices [Line Items]
Required statutory capital and surplus	668,794,000	[3]	657,865,000	[3]
Actual statutory capital and surplus	2,233,596,000	[2],[3]	2,244,505,000	[2],[3]
Statutory net income (loss)	155,751,000		124,310,000		106,510,000
RBC level for certain operating subsidiaries	100.00%
Maximum permitted dividends as a percentage of statutory policyholder surplus	10.00%
Maximum permitted dividends as a percentage of "Adjusted net investment income"	100.00%
Maximum dividend permitted without affidavit	196,200,000
Statutory earned surplus, amount	205,500,000		180,500,000
Number of property and casualty subsidiaries	7
Europe, UK, and other
Statutory Accounting Practices [Line Items]
Required statutory capital and surplus	1,604,721,000		1,970,909,000
Actual statutory capital and surplus	2,712,552,000	[2]	2,684,317,000	[2]
Statutory net income (loss)	215,787,000		1,465,000		144,829,000
Ireland
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus	1,100,000,000
Distributable reserves, amount	2,900,000,000
United Kingdom
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus	$ 1,200,000,000

[1] Required statutory capital and surplus at December 31, 2014 represents 100% Bermuda Solvency Capital Requirement (“BSCR”) level for the top Bermuda operating subsidiary, XL Insurance (Bermuda) Ltd, calculated on a consolidated basis (and therefore includes a BSCR requirement for all regions).

[2] Statutory assets in Bermuda include investments in other U.S. and international subsidiaries reported separately herein.

[3] Required statutory capital and surplus represents 100% Risk-Based Capital level for principal U.S. operating subsidiaries.