Investments (Securities Held In Unrealized Loss Position And Insured By Financial Guarantor) (Detail) - USD ($) $ in Millions		Jun. 30, 2015	Dec. 31, 2014
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value		$ 2,067	$ 2,071
Wrapped Securities [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value		141
Gross unrealized losses		(36)
Loss and loss adjustment expense reserves	[1]	76
Asset-backed [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value		254
Gross unrealized losses		(32)
Asset-backed [Member] | Wrapped Securities [Member] | Mbia Corp And National [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	[2]	104
Gross unrealized losses	[2]	(31)
Loss and loss adjustment expense reserves	[1],[2]	67
Mortgage-backed [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value		549
Gross unrealized losses		(14)
Mortgage-backed [Member] | Wrapped Securities [Member] | Mbia Corp And National [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	[2]	7
Gross unrealized losses	[2]	0
Loss and loss adjustment expense reserves	[1],[2]	9
Corporate Obligations [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value		561
Gross unrealized losses		(106)
Corporate Obligations [Member] | Wrapped Securities [Member] | Mbia Corp And National [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	[2]	6
Gross unrealized losses	[2]	0
Loss and loss adjustment expense reserves	[1],[2]	0
All Other Securities [Member] | Wrapped Securities [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value		24
Gross unrealized losses		(5)
Loss and loss adjustment expense reserves	[1]	0
All Other Securities [Member] | Wrapped Securities [Member] | Mbia Corp And National [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	[2]	23
Gross unrealized losses	[2]	(5)
Loss and loss adjustment expense reserves	[1],[2]	0
All Other Securities [Member] | Wrapped Securities [Member] | Other Insurers [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value		1
Gross unrealized losses		0
Loss and loss adjustment expense reserves	[1]	$ 0

[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.