Investments - Narrative (Details) $ in Thousands		3 Months Ended		9 Months Ended
	May. 01, 2014 USD ($)	Sep. 30, 2015 USD ($) positions	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) positions	Sep. 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		$ (40,681)	$ (51,286)	$ (127,365)	$ 423,179
Fixed maturities, at fair value		33,276,322		33,276,322		$ 29,359,034
Amortized cost of fixed maturities		$ 32,207,019		$ 32,207,019		$ 27,728,771
Percentage of Fixed Income Investment portfolio invested in below investment grade or not rated		2.10%		2.10%		3.00%
Percentage of Gross Unrealized losses in Fixed income securities portfolio related to securities below investment grade or not rated		15.90%		15.90%		24.90%
Available for sale securities, Gross unrealized losses		$ 325,781		$ 325,781		$ 213,576
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | positions		2,644		2,644
Available-for-sale Securities, Qualitative Disclosure, Number of Positions | positions		8,804		8,804
Pledged Assets Separately Reported, Other Debt Securities Available-for-sale or Held-for-investment		$ 18,800,000		$ 18,800,000		15,200,000
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Securities Sold		1,531	1,840	38,564	10,042
Corporate
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities		3,200
Medium term notes
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, at fair value		74,300		74,300		79,900
Amortized cost of fixed maturities		64,600		64,600		68,400
Structured Credit Securities
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities		30		30
Marketable Securities Unrealized Loss Other Than Temporary Impairments Amount		$ 200		$ 200
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		$ 8,000
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Securities Sold		1,300	900	$ 30,200	6,100
Foreign exchange losses
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities		19,600
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		2,200
Government Related Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities		2,000
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				(127,400)
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		29,637,961		29,637,961		24,177,469
Amortized cost of fixed maturities		29,144,400		29,144,400		23,427,432
Available for sale securities, Gross unrealized losses		325,781		325,781		213,576
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities		42,714	$ 1,144	69,878	$ 29,487
Excluding Life Funds Withheld Assets | RMBS - Non-Agency
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, at fair value		362,965		362,965		427,351
Amortized cost of fixed maturities		351,793		$ 351,793		$ 404,398
In A Loss Position For More Than 11 Months | Equities
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities		4,400
In a Loss Position Greater Than 50% of Amortized Cost | Equities
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities		$ 3,300