Investments - Narrative (Details) $ in Thousands		12 Months Ended
	May. 01, 2014 USD ($)	Dec. 31, 2015 USD ($) positions	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Schedule Of Marketable Securities [Line Items]
Cumulative adjustments recorded to value of future policy benefit reserves, amount		$ (170,688)	$ 400,456	$ 44,660
Fixed maturities, AFS, at fair value		32,257,589	29,359,034
Amortized cost of fixed maturities, available for sale		$ 31,517,654	$ 27,728,771
Percentage of fixed income portfolio invested in securities below investment grade		2.00%	3.00%
Percentage of gross unrealized losses relating to securities below investment grade		14.70%	24.90%
Pledged assets, amount		$ 18,300,000	$ 15,200,000
Gross unrealized losses		$ 369,975	213,576
Total number of positions - AFS | positions		8,729
AFS securities in unrealized loss position (number of positions) | positions		3,248
OTTI on investments, net of amounts transferred to other comprehensive income		$ 83,000	35,700
Credit loss impairments previously recognized on securities which matured, paid down, prepaid or were sold during the period		54,648	42,671
Equity securities, AFS, at fair value		878,919	868,292
Cost of equity securities, available for sale		834,079	763,833
Hedge funds
Schedule Of Marketable Securities [Line Items]
OTTI on investments, net of amounts transferred to other comprehensive income		4,000
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule Of Marketable Securities [Line Items]
OTTI on investments, net of amounts transferred to other comprehensive income		2,000
Corporate
Schedule Of Marketable Securities [Line Items]
OTTI on investments, net of amounts transferred to other comprehensive income		19,400	3,700
Fixed Income Funds Member
Schedule Of Marketable Securities [Line Items]
Cost of equity securities, available for sale		100,000
Structured Credit Securities [Member]
Schedule Of Marketable Securities [Line Items]
OTTI on investments, net of amounts transferred to other comprehensive income		1,300	4,300
Other Investments [Member]
Schedule Of Marketable Securities [Line Items]
OTTI on investments, net of amounts transferred to other comprehensive income		8,700	12,500
Currency losses
Schedule Of Marketable Securities [Line Items]
OTTI on investments, net of amounts transferred to other comprehensive income		23,600	4,300
Collateralized debt obligations ('CDO') [Member]
Schedule Of Marketable Securities [Line Items]
OTTI on investments, net of amounts transferred to other comprehensive income		8,000
XL Re Life (SAC) Ltd [Member]
Schedule Of Marketable Securities [Line Items]
Held To Maturity Securities Transferred Security Carrying Value	$ 2,800,000
Fixed maturities, held to maturity, gross unrealized gains	424,900
Fixed maturities, held to maturity, gross unrealized losses	0
Unrealized Gains (Losses) on Investments
Schedule Of Marketable Securities [Line Items]
Cumulative adjustments recorded to value of future policy benefit reserves, amount		(170,700)
Unrealized Gains (Losses) on Investments | XL Re Life (SAC) Ltd [Member]
Schedule Of Marketable Securities [Line Items]
Cumulative adjustments recorded to value of future policy benefit reserves, amount	$ 440,500
Exclude Life Funds Withheld Assets [Member]
Schedule Of Marketable Securities [Line Items]
Fixed maturities, AFS, at fair value		29,104,486	24,177,469
Amortized cost of fixed maturities, available for sale		28,839,622	23,427,432
Gross unrealized losses		369,975	213,576
Equity securities, AFS, at fair value		878,919	868,292
Cost of equity securities, available for sale		834,079	763,833
Exclude Life Funds Withheld Assets [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule Of Marketable Securities [Line Items]
Fixed maturities, AFS, at fair value		3,757,971	3,728,576
Amortized cost of fixed maturities, available for sale		3,697,756	3,625,171
Exclude Life Funds Withheld Assets [Member] | Equity securities
Schedule Of Marketable Securities [Line Items]
OTTI on investments, net of amounts transferred to other comprehensive income		15,954	10,944	$ 17
Exclude Life Funds Withheld Assets [Member] | RMBS - Non-Agency
Schedule Of Marketable Securities [Line Items]
Fixed maturities, AFS, at fair value		328,540	427,351
Amortized cost of fixed maturities, available for sale		319,876	404,398
Exclude Life Funds Withheld Assets [Member] | CMBS
Schedule Of Marketable Securities [Line Items]
Fixed maturities, AFS, at fair value		405,316	1,052,544
Amortized cost of fixed maturities, available for sale		401,713	1,033,819
Exclude Life Funds Withheld Assets [Member] | Collateralized debt obligations ('CDO') [Member]
Schedule Of Marketable Securities [Line Items]
Fixed maturities, AFS, at fair value		32,410	692,034
Amortized cost of fixed maturities, available for sale		$ 41,679	$ 717,544