Significant Accounting Policies (Details) - USD ($) $ / shares in Units, $ in Millions	6 Months Ended
	Jun. 30, 2017	Dec. 31, 2016	May 30, 2014
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Common shares, par value (in dollars per share)	$ 0.01	$ 0.01
Statement of cash flows, reclassification adjustment	$ 27.9
XL Ireland [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Common shares, par value (in dollars per share)	$ 0.01
XL Group Ltd [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Common shares, par value (in dollars per share)	$ 0.01
XL Re Life (SAC) Ltd
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Quota share reinsurance agreement, percentage			100.00%