Income Taxes (Narrative) (Details) (USD $)	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Percentage of tax on valuation allowance, tax exempt interest income from investments	35.00%
Federal statutory rate	35.00%
Capital loss carryforwards			$ 413,000,000
NOL carryforwards	782,000,000
Minimum tax credit carryforward	46,000,000
Cumulative net unrealized losses, excluding credit impairments, primarily related to insured credit derivatives	1,900,000,000
Insured credit derivatives	5,500,000,000
Unrealizable deferred tax assets	1,600,000,000
Decrease in cumulative ownership change	25.60%
Cumulative ownership shift	50.00%
Percentage of ownership of new owners	5.00%
Percentage of dispositions	5.00%
Taxable income projection, years	15Y
Maximum taxable income projection years	20Y
Deferred tax assets related to unrealized losses on investments	99,000,000
Defined testing period for ownership change, approximate years	3Y
Cumulative undistributed earnings	47,000,000	99,000,000
Non Variable Interest Entities [Member]
Deferred income taxes, net	1,574,000,000		908,000,000
Valuation allowance	366,000,000		376,000,000
Valuation allowance decrease	$ 10,000,000