Business Changes, Risks, Uncertainties and Accounting Developments (Details 2) (USD $) In Millions, unless otherwise specified						3 Months Ended
	May 08, 2012	May 08, 2012 Covered Transactions Transaction	Apr. 25, 2012 Covered Transactions	Jun. 30, 2012 Uninsured Tranches	May 08, 2012 Uninsured Tranches	Jun. 30, 2012 RMBS Transaction
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
Number of transactions insured		8
Loss sharing percentage, first layer		80.00%			60.00%
Maximum aggregate collateral losses up to which first layer of loss sharing will be applicatble		318.8			141.1
Minimum losses at which second later of loss sharing percentage becomes applicable		388.8			161.1
Maximum aggregate collateral losses up to which second layer of loss sharing will be applicable		600.0
Loss sharing percentage, second layer		85.00%			60.00%
Gross Par Outstanding			567.8	329.3
Number of transactions, against which litigations have been settled						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