Future Policy Benefit Reserve (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Liability for Future Policy Benefit, by Product Segment [Line Items]
Reinsurance recoverable from GCLR	$ (3,072,615)	$ (3,719,131)
Funds withheld on GreyCastle life retrocession arrangements (net of future policy benefit reserves recoverable: 2016 - $3,072,615; 2015 - $3,719,131)	998,968	914,629
Future policy benefit reserves are comprised of the following:
Traditional life	737,252	792,001
Annuities	2,768,795	3,371,499
Total future policy benefit reserves	$ 3,506,047	$ 4,163,500
Other information:
Average interest rate used for future policy benefits, percent	4.00%	3.30%
XL Re Life (SAC) Ltd [Member]
Liability for Future Policy Benefit, by Product Segment [Line Items]
Funds Held under Reinsurance Agreements, Liability	$ 4,071,583	$ 4,633,760
Reinsurance recoverable from GCLR	(3,072,615)	(3,719,131)
U.S. Term Life Reinsurance [Member]
Liability for Future Policy Benefit, by Product Segment [Line Items]
Reinsurance recoverable from GCLR	(270,238)	(284,481)
Other Life Retrocessions [Member]
Liability for Future Policy Benefit, by Product Segment [Line Items]
Reinsurance recoverable from GCLR	(10,997)	(13,801)
Corporate and other | XL Re Life (SAC) Ltd [Member]
Liability for Future Policy Benefit, by Product Segment [Line Items]
Future Policy Benefit Reserve Retention	$ 152,197	$ 146,087