Loss And Loss Adjustment Expense Reserves (RMBS Recoveries) (Narrative) (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Apr. 30, 2011	Dec. 31, 2010
Loss And Loss Adjustment Expense Reserves [Line Items]
Federal statutory rate	35.00%	35.00%
Estimated insurance recoveries, after income taxes	$ 2,100,000,000	$ 2,000,000,000
Percentage of recognized estimated recoveries in relationship to consolidated total shareholder's equity	111.00%	119.00%
Percentage of ineligible mortgage loan recoveries of statutory capital	112.00%	89.00%
Contract claims on ineligible mortgages	4,800,000,000
Aggregate of estimated potential recoveries	3,200,000,000
Settlement received for assured guaranty put-back claims			1,100,000,000
Bank of America repurchase requests resolved				8,000,000,000
Second-Lien RMBS Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Total estimated recoveries from ineligible loans	3,200,000,000
Insurance loss recoverable	2,100,000,000
Loan repurchase commitments	$ 1,100,000,000
First And Second Lien RMBS [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Percentage of ineligible mortgage loans	80.00%
RMBS And HELOC And CES [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Sum of probabilities assigned to all scenarios	100.00%
Current risk-free rate associated with underlying transaction, range, minimum	1.00%
Current risk-free rate associated with underlying transaction, range, maximum	2.20%