Guarantor Financial Information Guarantor Financial Information (Narrative) (Details)	12 Months Ended
	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Percentage ownership of subsidiaries	100.00%
XL Group Ltd
Condensed Financial Statements, Captions [Line Items]
Percentage ownership of subsidiaries	100.00%
XL Cayman
Condensed Financial Statements, Captions [Line Items]
Percentage ownership of subsidiaries	100.00%