Investments (Details 1) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis [Abstract]
Available-for-sale Securities, Debt Maturities, within One Year, Amortized Cost Basis	$ 294,720,000
Available-for-sale Securities, Debt Maturities, after One Through Five Years, Amortized Cost Basis	3,785,992,000
Available-for-sale Securities, Debt Maturities, after Five Through Ten Years, Amortized Cost Basis	6,592,768,000
Available-for-sale Securities, Debt Maturities, after Ten Years, Amortized Cost Basis	5,607,854,000
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis	3,278,098,000
Available for Sale at Fair value - Amortized cost	19,559,432,000	14,182,880,000
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Available-for-sale Securities, Debt Maturities, within One Year, Fair Value	299,389,000
Available-for-sale Securities, Debt Maturities, after One Through Five Years, Fair Value	3,983,272,000
Available-for-sale Securities, Debt Maturities, after Five Through Ten Years, Fair Value	7,198,997,000
Available-for-sale Securities, Debt Maturities, after Ten Years, Fair Value	7,377,434,000
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value	3,432,522,000
Fixed maturity securities available-for-sale	$ 22,291,614,000	$ 16,200,950,000

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