Loss And Loss Adjustment Expense Reserves (Schedule Of Losses And Loss Adjustment Expenses) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Loss And Loss Adjustment Expense Reserves [Line Items]
Policyholder Benefits And Claims Incurred Net	$ 50	$ 39	$ 149	$ 79
U S Public Finance Insurance [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Policyholder Benefits And Claims Incurred Net	28	(7)	46	(5)
Second-Lien RMBS [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Policyholder Benefits And Claims Incurred Net	44	24	78	52
First-Lien RMBS [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Policyholder Benefits And Claims Incurred Net	0	18	61	2
CDOs [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Policyholder Benefits And Claims Incurred Net	(23)	5	(46)	39
Other [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Policyholder Benefits And Claims Incurred Net	$ 1	$ (1)	$ 10	$ (9)