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Amortized Cost or Cost and Fair Value of Available For Sale Securities (Detail) (USD $)
Mar. 31, 2015
Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost or Cost $ 17,450,300,000us-gaap_AvailableForSaleSecuritiesAmortizedCost $ 17,446,100,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
Gross Unrealized Gains 839,400,000us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax 829,300,000us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Gross Unrealized Losses (52,400,000)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax (145,700,000)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Fair Value 18,237,300,000us-gaap_AvailableForSaleSecurities 18,129,700,000us-gaap_AvailableForSaleSecurities
Equity securities, cost 2,573,160,000us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis 2,366,035,000us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis
Equity securities, gross unrealized gains 495,300,000us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax 530,300,000us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Equity securities, gross unrealized losses (15,000,000)us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax (80,800,000)us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Equity securities, fair value 3,053,543,000us-gaap_AvailableForSaleSecuritiesEquitySecurities 2,815,484,000us-gaap_AvailableForSaleSecuritiesEquitySecurities
Debt securities, amortized cost 14,363,443,000us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis 14,364,430,000us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
Debt securities, gross unrealized gains 344,100,000us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax 299,000,000us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Debt securities, gross unrealized losses (37,400,000)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax (64,900,000)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Debt securities, fair value 14,670,207,000us-gaap_AvailableForSaleSecuritiesDebtSecurities 14,598,641,000us-gaap_AvailableForSaleSecuritiesDebtSecurities
Short-term Investments    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost or Cost 513,600,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_ShortTermInvestmentsMember		 715,600,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_ShortTermInvestmentsMember
Fair Value 513,600,000us-gaap_AvailableForSaleSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_ShortTermInvestmentsMember		 715,600,000us-gaap_AvailableForSaleSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_ShortTermInvestmentsMember
U.S. Government obligations    
Schedule of Available-for-sale Securities [Line Items]    
Debt securities, amortized cost 521,500,000us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentDebtSecuritiesMember		 541,200,000us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentDebtSecuritiesMember
Debt securities, gross unrealized gains 5,000,000us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentDebtSecuritiesMember		 3,400,000us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentDebtSecuritiesMember
Debt securities, gross unrealized losses (1,200,000)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentDebtSecuritiesMember		 (3,500,000)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentDebtSecuritiesMember
Debt securities, fair value 525,300,000us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentDebtSecuritiesMember		 541,100,000us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentDebtSecuritiesMember
Municipal bonds    
Schedule of Available-for-sale Securities [Line Items]    
Debt securities, amortized cost 5,032,700,000us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MunicipalBondsMember		 5,067,300,000us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MunicipalBondsMember
Debt securities, gross unrealized gains 144,100,000us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MunicipalBondsMember		 139,300,000us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MunicipalBondsMember
Debt securities, gross unrealized losses (9,100,000)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MunicipalBondsMember		 (9,100,000)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MunicipalBondsMember
Debt securities, fair value 5,167,700,000us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MunicipalBondsMember		 5,197,500,000us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MunicipalBondsMember
Foreign government obligations    
Schedule of Available-for-sale Securities [Line Items]    
Debt securities, amortized cost 793,200,000us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember		 876,700,000us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
Debt securities, gross unrealized gains 27,700,000us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember		 23,700,000us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
Debt securities, gross unrealized losses (100,000)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember		  
Debt securities, fair value 820,800,000us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember		 900,400,000us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
U.S. corporate bonds    
Schedule of Available-for-sale Securities [Line Items]    
Debt securities, amortized cost 2,072,800,000us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DomesticCorporateDebtSecuritiesMember		 2,136,500,000us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DomesticCorporateDebtSecuritiesMember
Debt securities, gross unrealized gains 50,300,000us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DomesticCorporateDebtSecuritiesMember		 39,500,000us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DomesticCorporateDebtSecuritiesMember
Debt securities, gross unrealized losses (12,600,000)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DomesticCorporateDebtSecuritiesMember		 (21,200,000)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DomesticCorporateDebtSecuritiesMember
Debt securities, fair value 2,110,500,000us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DomesticCorporateDebtSecuritiesMember		 2,154,800,000us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DomesticCorporateDebtSecuritiesMember
Foreign corporate bonds    
Schedule of Available-for-sale Securities [Line Items]    
Debt securities, amortized cost 1,367,300,000us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignCorporateDebtSecuritiesMember		 1,460,500,000us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignCorporateDebtSecuritiesMember
Debt securities, gross unrealized gains 49,300,000us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignCorporateDebtSecuritiesMember		 47,700,000us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignCorporateDebtSecuritiesMember
Debt securities, gross unrealized losses (2,200,000)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignCorporateDebtSecuritiesMember		 (4,500,000)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignCorporateDebtSecuritiesMember
Debt securities, fair value 1,414,400,000us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignCorporateDebtSecuritiesMember		 1,503,700,000us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignCorporateDebtSecuritiesMember
Mortgage and asset backed securities | RMBS    
Schedule of Available-for-sale Securities [Line Items]    
Debt securities, amortized cost 1,801,200,000us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_DebtSecurityAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= y_MortgageAndAssetBackedSecuritiesMember		 1,646,900,000us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_DebtSecurityAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= y_MortgageAndAssetBackedSecuritiesMember
Debt securities, gross unrealized gains 27,100,000us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_DebtSecurityAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= y_MortgageAndAssetBackedSecuritiesMember		 20,700,000us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_DebtSecurityAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= y_MortgageAndAssetBackedSecuritiesMember
Debt securities, gross unrealized losses (6,800,000)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_DebtSecurityAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= y_MortgageAndAssetBackedSecuritiesMember		 (11,700,000)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_DebtSecurityAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= y_MortgageAndAssetBackedSecuritiesMember
Debt securities, fair value 1,821,500,000us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_DebtSecurityAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= y_MortgageAndAssetBackedSecuritiesMember		 [1] 1,655,900,000us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_DebtSecurityAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= y_MortgageAndAssetBackedSecuritiesMember		 [1]
Mortgage and asset backed securities | CMBS    
Schedule of Available-for-sale Securities [Line Items]    
Debt securities, amortized cost 1,170,200,000us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_DebtSecurityAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= y_MortgageAndAssetBackedSecuritiesMember		 1,104,200,000us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_DebtSecurityAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= y_MortgageAndAssetBackedSecuritiesMember
Debt securities, gross unrealized gains 34,500,000us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_DebtSecurityAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= y_MortgageAndAssetBackedSecuritiesMember		 22,500,000us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_DebtSecurityAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= y_MortgageAndAssetBackedSecuritiesMember
Debt securities, gross unrealized losses (600,000)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_DebtSecurityAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= y_MortgageAndAssetBackedSecuritiesMember		 (1,400,000)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_DebtSecurityAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= y_MortgageAndAssetBackedSecuritiesMember
Debt securities, fair value 1,204,100,000us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_DebtSecurityAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= y_MortgageAndAssetBackedSecuritiesMember		 1,125,300,000us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_DebtSecurityAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= y_MortgageAndAssetBackedSecuritiesMember
Mortgage and asset backed securities | Other asset-backed securities    
Schedule of Available-for-sale Securities [Line Items]    
Debt securities, amortized cost 1,604,600,000us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_DebtSecurityAxis
= us-gaap_OtherDebtSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= y_MortgageAndAssetBackedSecuritiesMember		 [2] 1,531,200,000us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_DebtSecurityAxis
= us-gaap_OtherDebtSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= y_MortgageAndAssetBackedSecuritiesMember		 [2]
Debt securities, gross unrealized gains 6,100,000us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_DebtSecurityAxis
= us-gaap_OtherDebtSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= y_MortgageAndAssetBackedSecuritiesMember		 [2] 2,200,000us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_DebtSecurityAxis
= us-gaap_OtherDebtSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= y_MortgageAndAssetBackedSecuritiesMember		 [2]
Debt securities, gross unrealized losses (4,800,000)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_DebtSecurityAxis
= us-gaap_OtherDebtSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= y_MortgageAndAssetBackedSecuritiesMember		 [2] (13,500,000)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_DebtSecurityAxis
= us-gaap_OtherDebtSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= y_MortgageAndAssetBackedSecuritiesMember		 [2]
Debt securities, fair value 1,605,900,000us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_DebtSecurityAxis
= us-gaap_OtherDebtSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= y_MortgageAndAssetBackedSecuritiesMember		 [2] 1,519,900,000us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_DebtSecurityAxis
= us-gaap_OtherDebtSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= y_MortgageAndAssetBackedSecuritiesMember		 [2]
Common Stock    
Schedule of Available-for-sale Securities [Line Items]    
Equity securities, cost 2,573,200,000us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommonStockMember		 2,366,000,000us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommonStockMember
Equity securities, gross unrealized gains 495,300,000us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommonStockMember		 530,300,000us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommonStockMember
Equity securities, gross unrealized losses (15,000,000)us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommonStockMember		 (80,800,000)us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommonStockMember
Equity securities, fair value $ 3,053,500,000us-gaap_AvailableForSaleSecuritiesEquitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommonStockMember		 $ 2,815,484,000us-gaap_AvailableForSaleSecuritiesEquitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommonStockMember
[1] Primarily includes government agency pass-through securities guaranteed by a government agency or government sponsored enterprise, among other types of RMBS.
[2] Includes $907.1 million and $900.7 million of collateralized loan obligations as of March 31, 2015 and December 31, 2014, respectively.