Investments (Unrealized Loss Position And Insured By Financial Guarantor) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Total, Fair Value	$ 2,387		$ 6,954
Total, Unrealized Losses	(478)		(804)
Mortgage-Backed Securities [Member]
Total, Fair Value	401
Total, Unrealized Losses	(119)
Mortgage-Backed Securities [Member] | MBIA Corp. [Member]
Total, Fair Value	18	[1]
Total, Unrealized Losses	(5)	[1]
Mortgage-Backed Securities [Member] | Other [Member]
Total, Fair Value	239
Total, Unrealized Losses	(95)
Asset-Backed Securities [Member]
Total, Fair Value	639
Total, Unrealized Losses	(215)
Asset-Backed Securities [Member] | MBIA Corp. [Member]
Total, Fair Value	338	[1]
Total, Unrealized Losses	(78)	[1]
Loss and Loss Adjustment Expense Reserves	17	[1],[2]
Asset-Backed Securities [Member] | Other [Member]
Total, Fair Value	111
Total, Unrealized Losses	(24)
Corporate Obligations [Member]
Total, Fair Value	717
Total, Unrealized Losses	(106)
Corporate Obligations [Member] | MBIA Corp. [Member]
Total, Fair Value	97	[1]
Total, Unrealized Losses	(17)	[1]
Corporate Obligations [Member] | Other [Member]
Total, Fair Value	74
Total, Unrealized Losses	(15)
Other [Member] | MBIA Corp. [Member]
Total, Fair Value	102	[1]
Total, Unrealized Losses	(16)	[1]
Other [Member] | Other [Member]
Total, Fair Value	30
Wrapped Securities [Member]
Total, Fair Value	1,009
Total, Unrealized Losses	(250)
Loss and Loss Adjustment Expense Reserves	17	[2]
Wrapped Securities [Member] | Other [Member]
Total, Fair Value	132
Total, Unrealized Losses	(16)
Wrapped Securities [Member] | Mortgage-Backed Securities [Member]
Total, Fair Value	257
Total, Unrealized Losses	(100)
Wrapped Securities [Member] | Asset-Backed Securities [Member]
Total, Fair Value	449
Total, Unrealized Losses	(102)
Loss and Loss Adjustment Expense Reserves	17	[2]
Wrapped Securities [Member] | Corporate Obligations [Member]
Total, Fair Value	171
Total, Unrealized Losses	$ (32)

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

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