Investments - Narrative (Details) (USD $)	3 Months Ended			6 Months Ended
	Jun. 30, 2013 positions		Jun. 30, 2012	Jun. 30, 2013 positions		Jun. 30, 2012	Dec. 31, 2012
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	14.70%			14.70%			37.70%
Fixed maturities, at fair value	$ 26,455,103,000			$ 26,455,103,000			$ 27,846,920,000
Fixed maturities, held to maturity	2,686,994,000			2,686,994,000			2,814,447,000
Fair value of held to maturity securities	2,978,981,000			2,978,981,000			3,262,804,000
Amortized cost of fixed maturities	26,016,208,000			26,016,208,000			26,544,806,000
Equity securities, at fair value	916,008,000			916,008,000			649,359,000
Cost of equity securities	873,465,000			873,465,000			617,486,000
Percentage of Fixed Income Investment portfolio invested in below investment grade or not rated	2.80%			2.80%			2.90%
Pledged Assets Separately Reported, Other Debt Securities Available-for-sale or Held-for-investment	15,900,000,000			15,900,000,000			16,900,000,000
Gross Unrealized Losses Related Changes In Estimated Fair Value	461,089,000			461,089,000			282,812,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	2,162			2,162
Available-for-sale Securities, Qualitative Disclosure, Number of Positions	7,525			7,525
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses	3,261,000			3,261,000			2,681,000
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	6			6
Held-to-maturity Securities, Qualitative Disclosure, Number of Positions	204			204
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Securities Sold	55,144,000		36,783,000	61,619,000		53,978,000
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities	2,389,000		28,193,000	7,027,000		49,158,000
Government Related Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Cost Or Amortized Cost	2,357,000,000			2,357,000,000			1,912,700,000
Marketable Securities	2,374,500,000			2,374,500,000			1,988,500,000
Agency Securities
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Cost Or Amortized Cost	297,200,000			297,200,000			404,300,000
Marketable Securities	321,600,000			321,600,000			446,700,000
Covered bonds
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Cost Or Amortized Cost	8,000,000			8,000,000
Fixed maturities, at fair value	550,900,000			550,900,000			647,100,000
Fixed maturities, held to maturity							8,400,000
Fair value of held to maturity securities							8,600,000
Amortized cost of fixed maturities	523,500,000			523,500,000			605,400,000
Marketable Securities	8,200,000			8,200,000
Corporate
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, at fair value	10,079,475,000	[1],[2]		10,079,475,000	[1],[2]		10,482,000,000	[1],[2]
Fixed maturities, held to maturity	1,312,332,000			1,312,332,000			1,425,320,000
Fair value of held to maturity securities	1,428,346,000			1,428,346,000			1,615,397,000
Amortized cost of fixed maturities	9,752,465,000	[1],[2]		9,752,465,000	[1],[2]		9,837,962,000	[1],[2]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses	2,122,000			2,122,000			794,000
Medium term notes
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, at fair value	149,400,000			149,400,000			194,300,000
Amortized cost of fixed maturities	150,200,000			150,200,000			194,800,000
Tier One And Upper Tier Two Securities
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Cost Or Amortized Cost	298,600,000			298,600,000			327,600,000
Marketable Securities	281,400,000			281,400,000			308,500,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	17,200,000			17,200,000			19,100,000
Fixed income funds
Schedule of Available-for-sale Securities [Line Items]
Equity securities, at fair value	91,300,000			91,300,000			101,900,000
Cost of equity securities	100,000,000			100,000,000			100,000,000
Structured Credit Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities	3,700,000			3,700,000
Impaired Investment Cumulative Fair Value Decline Percentage Amortized Cost	50.00%			50.00%
Marketable Securities Realized Gain Loss Other Than Temporary Impairments Amount Total	12,800,000			12,800,000
RMBS - Non-Agency
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, at fair value	406,402,000			406,402,000			647,733,000
Fixed maturities, held to maturity	62,925,000			62,925,000			83,205,000
Fair value of held to maturity securities	67,749,000			67,749,000			93,707,000
Amortized cost of fixed maturities	418,458,000			418,458,000			678,469,000
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses	0			0			0
Marketable Securities Realized Gain Loss Other Than Temporary Impairments Amount Total	400,000			400,000
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Securities Sold	54,400,000		17,600,000	60,200,000		26,600,000
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities	2,000,000
Foreign Currency Adjustments
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities	400,000
CMBS
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, at fair value	1,129,072,000			1,129,072,000			1,077,251,000
Fixed maturities, held to maturity	136,193,000			136,193,000			12,751,000
Fair value of held to maturity securities	150,932,000			150,932,000			14,799,000
Amortized cost of fixed maturities	1,093,641,000			1,093,641,000			1,010,794,000
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses	0			0			0
Marketable Securities Realized Gain Loss Other Than Temporary Impairments Amount Total	600,000			600,000
Core Cdo Holdings
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Realized Gain Loss Other Than Temporary Impairments Amount Total	$ 11,900,000			$ 11,900,000

[1] Included within Corporate are certain medium term notes supported primarily by pools of European investment grade credit with varying degrees of leverage. The notes have a fair value of $149.4 million and an amortized cost of $150.2 million. These notes allow the investor to participate in cash flows of the underlying bonds including certain residual values, which could serve to either decrease or increase the ultimate values of these notes.

[2] Included within Corporate are Tier One and Upper Tier Two securities, representing committed term debt and hybrid instruments, which are senior to the common and preferred equities of the financial institutions. These securities have a fair value of $281.4 million and an amortized cost of $298.6 million at June 30, 2013.