Business Changes, Risks, Uncertainties and Accounting Developments (Details 2) (Deutsche Bank Agreement, USD $) In Millions, unless otherwise specified	1 Months Ended
	May 31, 2012 Transaction	May 08, 2012	Apr. 25, 2012
Financial guarantee obligations
Cash payment to be received		$ 165.6
Eligible assets to be placed in trust to collateralize the obligations of a reinsurance affiliate		282.7
Covered Transactions
Financial guarantee obligations
Number of transactions insured	8
Loss sharing percentage, first layer		80.00%
Maximum aggregate collateral losses up to which first layer of loss sharing will be applicable		318.8
Minimum losses at which second layer of loss sharing percentage becomes applicable		388.8
Loss sharing percentage, second layer		85.00%
Maximum aggregate collateral losses up to which second layer of loss sharing will be applicable		600.0
Gross Par Outstanding			581
Uninsured Tranches
Financial guarantee obligations
Loss sharing percentage, first layer		60.00%
Maximum aggregate collateral losses up to which first layer of loss sharing will be applicable		141.1
Minimum losses at which second layer of loss sharing percentage becomes applicable		161.1
Loss sharing percentage, second layer		60.00%
Gross Par Outstanding			337
Number of Covered Transactions in which certain Uninsured Tranches have been covered		3
Minimum losses at which third layer of loss sharing percentage becomes applicable		185.1
Loss sharing percentage, third layer		100.00%
Maximum aggregate collateral losses up to which third layer of loss sharing will be applicable		$ 247.8
RMBS
Financial guarantee obligations
Number of transactions, against which litigations have been settled	3