Guarantor Financial Information Narrative (Details)	6 Months Ended
	Jun. 30, 2018
Condensed Financial Statements, Captions [Line Items]
Percentage ownership of subsidiaries	100.00%
XL Group Ltd [Member]
Condensed Financial Statements, Captions [Line Items]
Percentage ownership of subsidiaries	100.00%
XL Cayman [Member]
Condensed Financial Statements, Captions [Line Items]
Percentage ownership of subsidiaries	100.00%