Investments - Narrative (Details) $ in Thousands		3 Months Ended		6 Months Ended
	May. 01, 2014 USD ($)	Jun. 30, 2015 USD ($) positions	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) positions	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Change in adjustments related to future policy benefit reserves, net of tax		$ (26,328)	$ 440,461	$ (86,684)	$ 474,465
Fixed maturities, at fair value		33,767,991		33,767,991		$ 29,359,034
Amortized cost of fixed maturities		$ 32,699,709		$ 32,699,709		$ 27,728,771
Percentage of Fixed Income Investment portfolio invested in below investment grade or not rated		2.50%		2.50%		3.00%
Percentage of Gross Unrealized losses in Fixed income securities portfolio related to securities below investment grade or not rated		14.80%		14.80%		24.90%
Available for sale securities, Gross unrealized losses		$ 282,751		$ 282,751		$ 213,576
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | positions		2,944		2,944
Available-for-sale Securities, Qualitative Disclosure, Number of Positions | positions		8,969		8,969
Pledged Assets Separately Reported, Other Debt Securities Available-for-sale or Held-for-investment		$ 18,400,000		$ 18,400,000		15,200,000
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Securities Sold		8,495	3,322	37,034	7,571
Corporate
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities		4,800
Medium term notes
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, at fair value		75,300		75,300		79,900
Amortized cost of fixed maturities		64,500		64,500		68,400
Alternative Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities		4,000
Structured Credit Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities		6,900		6,900
Marketable Securities Unrealized Loss Other Than Temporary Impairments Amount		$ 8,800		$ 8,800
Impaired Investment Cumulative Fair Value Decline Percentage Amortized Cost		50.00%		50.00%
RMBS - Non-Agency
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities		$ 200
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Securities Sold		1,700	2,500	$ 28,900	5,200
Foreign Currency Adjustments [Member]
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities		800
Equities
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities		300
Other investments
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities		6,500
XL Re Life (SAC) Ltd
Schedule of Available-for-sale Securities [Line Items]
Held To Maturity Securities Transferred Security Carrying Value	$ 2,800,000
Unrealized gains on held to maturity investment portfolio at time of transfer to available for sale, net of tax	424,900
Fixed maturites held to maturity, gross unrealized losses	0
Unrealized gains (losses) on investments
Schedule of Available-for-sale Securities [Line Items]
Change in adjustments related to future policy benefit reserves, net of tax				(86,700)
Unrealized gains (losses) on investments | XL Re Life (SAC) Ltd
Schedule of Available-for-sale Securities [Line Items]
Change in adjustments related to future policy benefit reserves, net of tax	$ 440,500
Excluding Life Funds Withheld Assets
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, at fair value		29,770,903		29,770,903		24,177,469
Amortized cost of fixed maturities		29,310,791		29,310,791		23,427,432
Available for sale securities, Gross unrealized losses		282,751		282,751		213,576
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities		16,588	$ 24,616	27,164	$ 28,343
Excluding Life Funds Withheld Assets | RMBS - Non-Agency
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, at fair value		372,271		372,271		427,351
Amortized cost of fixed maturities		$ 361,661		$ 361,661		$ 404,398