Loss And Loss Adjustment Expense Reserves (Schedule Of Losses And Loss Adjustment Expenses) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Loss And Loss Adjustment Expense Reserves [Line Items]
Losses and LAE related to actual and expected payments	$ 479
Recoveries of actual and expected payments	(428)
Gross losses incurred	51
Reinsurance	(1)
Losses and LAE	50
Second-Lien RMBS Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Losses and LAE related to actual and expected payments	220
Recoveries of actual and expected payments	(371)
Gross losses incurred	(151)
Reinsurance
Losses and LAE	(151)
First-Lien RMBS Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Losses and LAE related to actual and expected payments	147
Recoveries of actual and expected payments	1
Gross losses incurred	148
Reinsurance	(1)
Losses and LAE	147
Other [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Losses and LAE related to actual and expected payments	112	[1]
Recoveries of actual and expected payments	(58)	[1]
Gross losses incurred	54	[1]
Reinsurance		[1]
Losses and LAE	$ 54	[1]

[1] Primarily financial guarantee CMBS.