Investments (Securities Held In Unrealized Loss Position And Insured By Financial Guarantor) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	$ 3,457		$ 1,284
Gross unrealized losses	(229)		(152)
Wrapped Securities [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	301
Gross unrealized losses	(72)
Loss and loss adjustment expense reserves	16	[1]
Asset-backed [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	208
Gross unrealized losses	(72)
Asset-backed [Member] | Wrapped Securities [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	153
Gross unrealized losses	(59)
Loss and loss adjustment expense reserves	16	[1]
Asset-backed [Member] | Wrapped Securities [Member] | Mbia Corp And National [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	144	[2]
Gross unrealized losses	(55)	[2]
Loss and loss adjustment expense reserves	16	[1],[2]
Asset-backed [Member] | Wrapped Securities [Member] | Other Insurers [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	9
Gross unrealized losses	(4)
Loss and loss adjustment expense reserves	0	[1]
Mortgage-backed [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	907
Gross unrealized losses	(37)
Mortgage-backed [Member] | Wrapped Securities [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	9
Gross unrealized losses	0
Loss and loss adjustment expense reserves	0	[1]
Mortgage-backed [Member] | Wrapped Securities [Member] | Mbia Corp And National [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	5	[2]
Gross unrealized losses	0	[2]
Loss and loss adjustment expense reserves	0	[1],[2]
Mortgage-backed [Member] | Wrapped Securities [Member] | Other Insurers [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	4
Gross unrealized losses	0
Loss and loss adjustment expense reserves	0	[1]
Corporate Obligations [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	870
Gross unrealized losses	(38)
Corporate Obligations [Member] | Wrapped Securities [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	6
Gross unrealized losses	(2)
Loss and loss adjustment expense reserves	0	[1]
Corporate Obligations [Member] | Wrapped Securities [Member] | Mbia Corp And National [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	0	[2]
Gross unrealized losses	0	[2]
Loss and loss adjustment expense reserves	0	[1],[2]
Corporate Obligations [Member] | Wrapped Securities [Member] | Other Insurers [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	6
Gross unrealized losses	(2)
Loss and loss adjustment expense reserves	0	[1]
All Other Securities [Member] | Wrapped Securities [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	133
Gross unrealized losses	(11)
Loss and loss adjustment expense reserves	0	[1]
All Other Securities [Member] | Wrapped Securities [Member] | Mbia Corp And National [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	102	[2]
Gross unrealized losses	(10)	[2]
Loss and loss adjustment expense reserves	0	[1],[2]
All Other Securities [Member] | Wrapped Securities [Member] | Other Insurers [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	31
Gross unrealized losses	(1)
Loss and loss adjustment expense reserves	$ 0	[1]

[1] Insurance loss reserve estimates are based on the proportion of par value owned to the total amount of par value insured.

[2] Includes investments insured by MBIA Corp. and National.