Investments (Securities Held In Unrealized Loss Position And Insured By Financial Guarantor) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	$ 2,991		$ 3,457
Gross unrealized losses	(167)		(229)
Wrapped Securities [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	224
Gross unrealized losses	(63)
Loss and loss adjustment expense reserves	18	[1]
Asset-backed [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	199
Gross unrealized losses	(67)
Asset-backed [Member] | Wrapped Securities [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	147
Gross unrealized losses	(56)
Loss and loss adjustment expense reserves	18	[1]
Asset-backed [Member] | Wrapped Securities [Member] | Mbia Corp And National [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	139	[2]
Gross unrealized losses	(54)	[2]
Loss and loss adjustment expense reserves	18	[1],[2]
Asset-backed [Member] | Wrapped Securities [Member] | Other Insurers [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	8
Gross unrealized losses	(2)
Loss and loss adjustment expense reserves	0	[1]
Mortgage-backed [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	828
Gross unrealized losses	(27)
Mortgage-backed [Member] | Wrapped Securities [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	7
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	2
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	897
Gross unrealized losses	(34)
Corporate Obligations [Member] | Wrapped Securities [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	6
Gross unrealized losses	(1)
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	(1)
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	64
Gross unrealized losses	(6)
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	64	[2]
Gross unrealized losses	(6)	[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	0
Gross unrealized losses	0
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.