Guarantor Financial Information Narrative (Details) $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($)
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%
XL- Bermuda/Ireland
Condensed Financial Statements, Captions [Line Items]
Investments in subsidiaries	$ 0.5