Schedule II - Condensed Financial Information of Registrant (Condensed Balance Sheets) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2012 Xl Group PLC	Dec. 31, 2011 Xl Group PLC	Dec. 31, 2010 Xl Group PLC	Jun. 30, 2010 Xl Group PLC
ASSETS
Cash and cash equivalents	$ 2,618,378	$ 3,825,125	$ 3,022,868	$ 3,643,697	$ 10,961	$ 1,644	$ 2,816	$ 61
Amounts due from subsidiaries					0	80,841
Investments in subsidiaries on an equity basis					10,601,648	9,344,521
Other assets	582,765	670,895			3,241	3,797
Total assets	45,387,779	44,665,265			10,615,850	9,430,803
Liabilities:
Amounts due to subsidiaries					86,012	0
Accounts payable and accrued liabilities					19,766	19,145
Total liabilities	33,531,382	33,909,135			105,778	19,145
Commitments and Contingencies
Shareholders' equity:
Ordinary shares, 999,990,000 authorized, par value $0.01; issued and outstanding: (2012, 298,681,576; 2011, 315,645,796)	2,987	3,156			2,987	3,156
Additional paid-in capital					8,584,753	8,938,679
Accumulated other comprehensive income	1,520,011	583,064	100,795		1,520,011	583,064
Retained earnings (deficit)	402,321	(113,241)			402,321	(113,241)
Shareholders' equity attributable to XL Group plc	10,510,072	9,411,658			10,510,072	9,411,658
Total liabilities and shareholders' equity	$ 45,387,779	$ 44,665,265			$ 10,615,850	$ 9,430,803
Parenthetical information:
Ordinary shares, shares authorized (in shares)	999,990,000	999,990,000			999,990,000	999,990,000
Ordinary shares, par value (in dollars per share)	$ 0.01	$ 0.01			$ 0.01	$ 0.01
Ordinary shares, shares issued (in shares)	298,681,573	315,645,796			298,681,573	315,645,796
Ordinary shares, shares outstanding (in shares)	298,681,573	315,645,796	316,396,000		298,681,573	315,645,796