Reinsurance - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Liability for Future Policy Benefit, by Product Segment [Line Items]
Reinsurance recoverable from GCLR	$ 3,719,131	$ 4,265,678
Reinsurance recoveries on losses and loss expenses recorded during period	1,600,000	700,000	$ 700,000
Total reinsurance assets	5,700,000	3,600,000
Reinsurance receivable on paid losses	418,666	131,519
Unpaid losses and loss expenses recoverable	5,262,706	3,429,368
Total allowance for uncollectible reinsurance	82,145	64,439
Collateral held related to reinsurance recoverables	3,800,000	2,000,000
Total allowance recorded relating to reinsurance recoverables	58,200	42,300
Total allowance recorded relating to reinsurance balances receivable	23,900	22,100
U.S. Term Life Reinsurance [Member]
Liability for Future Policy Benefit, by Product Segment [Line Items]
Reinsurance recoverable from GCLR	284,481	0
XL Re Life (SAC) Ltd [Member]
Liability for Future Policy Benefit, by Product Segment [Line Items]
Reinsurance recoverable from GCLR	$ 3,719,131	$ 4,265,678