Loss And Loss Adjustment Expense Reserves (Schedule Of Losses And Loss Adjustment Expenses) (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Loss And Loss Adjustment Expense Reserves [Line Items]
Losses and LAE related to actual and expected payments	$ 453
Recoveries of actual and expected payments	(123)
Gross losses incurred	330
Reinsurance
Losses and LAE	330
Second-Lien RMBS Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Losses and LAE related to actual and expected payments	180
Recoveries of actual and expected payments	(74)
Gross losses incurred	106
Reinsurance
Losses and LAE	106
Other [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Losses and LAE related to actual and expected payments	273	[1]
Recoveries of actual and expected payments	(49)	[1]
Gross losses incurred	224	[1]
Reinsurance		[1]
Losses and LAE	$ 224	[1]

[1] Primarily first-lien RMBS and financial guarantee CMBS.