Investments (Details 5) (USD $)	Jun. 30, 2012	Dec. 31, 2011
Amortized Cost
Due within one year	$ 388,900,000
Due after one year through five years	1,408,700,000
Due after five years through 10 years	2,373,500,000
Due after 10 years	3,569,800,000
Total	9,618,789,000	9,638,404,000
Estimated Fair Value
Due within one year	390,100,000
Due after one year through five years	1,479,800,000
Due after five years through 10 years	2,599,300,000
Due after 10 years	3,856,200,000
Total	10,207,514,000	10,141,850,000
Fair value of the securities purchased exchanged in connection with Greek debt restructuring contracts	193,200,000
Par of the securities purchased exchanged in connection with Greek debt restructuring	220,400,000
Fixed maturity securities held under trust for the benefit of reinsured companies	393,400,000	380,100,000
Eligible securities deposited for the benefit of policyholders	26,900,000	23,900,000
Fixed maturity investments in a segregated portfolio primarily to provide collateral for a LOC	3,500,000	3,500,000
Cash deposited into trust for the benefit of the reinsurers	21,800,000
Fair market value of company's pledged securities	687,900,000	779,900,000
Fair value of the securities purchased to mitigate insured losses	256,900,000
Par of the securities purchased to mitigate insured losses	851,600,000
RMBS
Amortized Cost
Total	1,422,000,000
Estimated Fair Value
Total	1,395,600,000
CMBS
Amortized Cost
Total	455,900,000
Estimated Fair Value
Total	$ 486,500,000