Investments - Narrative (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014 positions	Jun. 30, 2013	Jun. 30, 2014 positions	Jun. 30, 2013	May 01, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Unrealized gains on held to maturity investment portfolio at time of transfer to available for sale, net of tax	$ 0		$ 0		$ 424,861,000	$ 274,150,000
Fixed maturites held to maturity, gross unrealized losses	0		0		0	1,610,000
Fixed maturities, at fair value	30,442,921,000		30,442,921,000			27,500,136,000
Percentage of Gross Unrealized losses in Fixed income securities portfolio related to securities below investment grade or not rated	22.00%		22.00%			12.40%
Investments In Structured Transactions Not Carried at Fair Value	275,821,000		275,821,000			294,048,000
Fixed maturities, held to maturity	0		0			2,858,695,000
Fair value of held to maturity securities	0		0			3,131,235,000
Amortized cost of fixed maturities	29,065,531,000		29,065,531,000			27,111,874,000
Equity securities, at fair value	988,710,000		988,710,000			1,040,237,000
Cost of equity securities	839,716,000		839,716,000			903,201,000
Percentage of Fixed Income Investment portfolio invested in below investment grade or not rated	2.80%		2.80%			2.60%
Pledged Assets Separately Reported, Other Debt Securities Available-for-sale or Held-for-investment	16,100,000,000		16,100,000,000			15,500,000,000
Available for sale securities, Gross unrealized losses	169,245,000		169,245,000			437,036,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	1,385		1,385
Available-for-sale Securities, Qualitative Disclosure, Number of Positions	7,668		7,668
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Securities Sold	3,322,000	55,144,000	7,571,000	61,619,000
Government Related Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Cost Or Amortized Cost	1,679,100,000		1,679,100,000			2,241,500,000
Marketable Securities	1,721,800,000		1,721,800,000			2,275,600,000
Agency Securities
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Cost Or Amortized Cost	230,200,000		230,200,000			267,000,000
Marketable Securities	256,800,000		256,800,000			284,300,000
Covered bonds
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, at fair value	763,600,000		763,600,000			553,100,000
Fixed maturities, held to maturity						8,600,000
Fair value of held to maturity securities						8,700,000
Amortized cost of fixed maturities	737,000,000		737,000,000			526,400,000
Corporate
Schedule of Available-for-sale Securities [Line Items]
Unrealized gains on held to maturity investment portfolio at time of transfer to available for sale, net of tax						113,179,000
Fixed maturites held to maturity, gross unrealized losses						968,000
Fixed maturities, at fair value						11,125,830,000
Fixed maturities, held to maturity						1,386,863,000
Fair value of held to maturity securities						1,499,074,000
Amortized cost of fixed maturities						10,802,332,000
Medium term notes
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, at fair value	155,900,000		155,900,000			154,600,000
Amortized cost of fixed maturities	143,600,000		143,600,000			147,700,000
Tier One And Upper Tier Two Securities
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Cost Or Amortized Cost	32,600,000		32,600,000			286,200,000
Marketable Securities	28,100,000		28,100,000			282,200,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In Investments	4,500,000		4,500,000			4,000,000
Fixed income funds
Schedule of Available-for-sale Securities [Line Items]
Equity securities, at fair value	92,100,000		92,100,000			87,400,000
Cost of equity securities	92,100,000		92,100,000			100,000,000
Structured Credit Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities	4,600,000		4,600,000
Impaired Investment Cumulative Fair Value Decline Percentage Amortized Cost	50.00%		50.00%
Marketable Securities Unrealized Loss Other Than Temporary Impairments Amount	10,600,000		10,600,000
RMBS - Non-Agency
Schedule of Available-for-sale Securities [Line Items]
Unrealized gains on held to maturity investment portfolio at time of transfer to available for sale, net of tax						4,985,000
Fixed maturites held to maturity, gross unrealized losses						0
Fixed maturities, at fair value						398,768,000
Fixed maturities, held to maturity	0		0			66,987,000
Fair value of held to maturity securities						71,972,000
Amortized cost of fixed maturities						396,798,000
Marketable Securities Unrealized Loss Other Than Temporary Impairments Amount	200,000		200,000
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Securities Sold	2,500,000	54,400,000	5,200,000	60,200,000
CMBS
Schedule of Available-for-sale Securities [Line Items]
Unrealized gains on held to maturity investment portfolio at time of transfer to available for sale, net of tax						11,864,000
Fixed maturites held to maturity, gross unrealized losses						0
Fixed maturities, at fair value						1,246,795,000
Fixed maturities, held to maturity	0		0			144,924,000
Fair value of held to maturity securities						156,788,000
Amortized cost of fixed maturities						1,223,313,000
Core Cdo Holdings
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Unrealized Loss Other Than Temporary Impairments Amount	10,400,000		10,400,000
XL Re Life (SAC) Ltd [Member]
Schedule of Available-for-sale Securities [Line Items]
Held To Maturity Securities Transferred Security Carrying Value	2,800,000,000		2,800,000,000
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	440,461,000	32,900,000	474,461,000	32,900,000
Excluding Life Funds Withheld Assets
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, at fair value	24,998,550,000		24,998,550,000
Amortized cost of fixed maturities	24,226,460,000		24,226,460,000
Available for sale securities, Gross unrealized losses	169,245,000		169,245,000
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities	24,616,000	2,389,000	28,343,000	7,027,000
Excluding Life Funds Withheld Assets | Corporate
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, at fair value	9,727,624,000		9,727,624,000
Amortized cost of fixed maturities	9,345,654,000		9,345,654,000
Excluding Life Funds Withheld Assets | RMBS - Non-Agency
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, at fair value	415,503,000		415,503,000
Amortized cost of fixed maturities	395,629,000		395,629,000
Excluding Life Funds Withheld Assets | 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	12,500,000
Excluding Life Funds Withheld Assets | CMBS
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, at fair value	1,124,287,000		1,124,287,000
Amortized cost of fixed maturities	1,098,149,000		1,098,149,000
Excluding Life Funds Withheld Assets | Equities
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities	$ 10,300,000