Investments - Narrative (Details) (USD $)	3 Months Ended
	Mar. 31, 2014 positions	Mar. 31, 2013	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Percentage of Gross Unrealized losses in Fixed income securities portfolio related to securities below investment grade or not rated	15.00%		12.40%
Fixed maturities, at fair value	$ 27,139,824,000		$ 27,500,136,000
Investments In Structured Transactions Not Carried at Fair Value	288,047,000		294,048,000
Fixed maturities, held to maturity	2,854,487,000		2,858,695,000
Fair value of held to maturity securities	3,209,175,000		3,131,235,000
Amortized cost of fixed maturities	26,485,164,000		27,111,874,000
Equity securities, at fair value	1,055,393,000		1,040,237,000
Cost of equity securities	907,952,000		903,201,000
Percentage of Fixed Income Investment portfolio invested in below investment grade or not rated	2.50%		2.60%
Pledged Assets Separately Reported, Other Debt Securities Available-for-sale or Held-for-investment	15,600,000,000		15,500,000,000
Available for sale securities, Gross unrealized losses	308,021,000		437,036,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	1,912
Available-for-sale Securities, Qualitative Disclosure, Number of Positions	7,848
Fixed maturites held to maturity, gross unrealized losses	190,000		1,610,000
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	2
Held-to-maturity Securities, Qualitative Disclosure, Number of Positions	201
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Securities Sold	3,348,000	6,475,000
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities	3,727,000	4,638,000
Government Related Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Cost Or Amortized Cost	2,301,800,000		2,241,500,000
Marketable Securities	2,365,000,000		2,275,600,000
Agency Securities
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Cost Or Amortized Cost	238,000,000		267,000,000
Marketable Securities	261,500,000		284,300,000
Covered bonds
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, at fair value	537,500,000		553,100,000
Fixed maturities, held to maturity	8,600,000		8,600,000
Fair value of held to maturity securities	8,900,000		8,700,000
Amortized cost of fixed maturities	508,300,000		526,400,000
Corporate
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, at fair value	11,108,505,000		11,125,830,000
Fixed maturities, held to maturity	1,376,931,000		1,386,863,000
Fair value of held to maturity securities	1,512,650,000		1,499,074,000
Amortized cost of fixed maturities	10,697,760,000		10,802,332,000
Fixed maturites held to maturity, gross unrealized losses	190,000		968,000
Medium term notes
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, at fair value	154,700,000		154,600,000
Amortized cost of fixed maturities	146,200,000		147,700,000
Tier One And Upper Tier Two Securities
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Cost Or Amortized Cost	281,300,000		286,200,000
Marketable Securities	279,800,000		282,200,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In Investments	1,600,000		4,000,000
Fixed income funds
Schedule of Available-for-sale Securities [Line Items]
Equity securities, at fair value	89,100,000		87,400,000
Cost of equity securities	100,900,000		100,000,000
Structured Credit Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities	4,800,000
Impaired Investment Cumulative Fair Value Decline Percentage Amortized Cost	50.00%
Marketable Securities Unrealized Loss Other Than Temporary Impairments Amount	11,300,000
RMBS - Non-Agency
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, at fair value	401,393,000		398,768,000
Fixed maturities, held to maturity	67,037,000		66,987,000
Fair value of held to maturity securities	73,780,000		71,972,000
Amortized cost of fixed maturities	389,181,000		396,798,000
Fixed maturites held to maturity, gross unrealized losses	0		0
Marketable Securities Unrealized Loss Other Than Temporary Impairments Amount	200,000
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Securities Sold	2,700,000	5,800,000
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities	2,200,000
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	1,500,000
CMBS
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, at fair value	1,198,312,000		1,246,795,000
Fixed maturities, held to maturity	145,005,000		144,924,000
Fair value of held to maturity securities	160,220,000		156,788,000
Amortized cost of fixed maturities	1,172,597,000		1,223,313,000
Fixed maturites held to maturity, gross unrealized losses	0		0
Marketable Securities Unrealized Loss Other Than Temporary Impairments Amount	500,000
Core Cdo Holdings
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Unrealized Loss Other Than Temporary Impairments Amount	$ 10,700,000