Investments (Unrealized Loss Position And Insured By Financial Guarantor) (Details) (USD $) In Millions	Sep. 30, 2011		Dec. 31, 2010
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	$ 2,549		$ 6,954
Total, Unrealized Losses	567		804
Mortgage-Backed Securities [Member] | Wrapped Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	277
Total, Unrealized Losses	(102)
Loss and Loss Adjustment Expense Reserves	1	[1]
Asset-Backed Securities [Member] | Wrapped Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	442
Total, Unrealized Losses	(104)
Loss and Loss Adjustment Expense Reserves	22	[1]
Wrapped Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	1,149
Total, Unrealized Losses	(255)
Loss and Loss Adjustment Expense Reserves	23	[1]
Wrapped Securities [Member] | All Others [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	241
Total, Unrealized Losses	(17)
Wrapped Securities [Member] | Corporate Obligations [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	189
Total, Unrealized Losses	(32)
Mortgage-Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	450
Total, Unrealized Losses	(121)
Mortgage-Backed Securities [Member] | MBIA [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	18	[2]
Total, Unrealized Losses	(5)	[2]
Loss and Loss Adjustment Expense Reserves	1	[1],[2]
Mortgage-Backed Securities [Member] | All Others [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	259
Total, Unrealized Losses	(97)
Asset-Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	723
Total, Unrealized Losses	285
Asset-Backed Securities [Member] | MBIA [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	323	[2]
Total, Unrealized Losses	(80)	[2]
Loss and Loss Adjustment Expense Reserves	22	[1],[2]
Asset-Backed Securities [Member] | All Others [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	119
Total, Unrealized Losses	(24)
All Others [Member] | Corporate Obligations [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	54
Total, Unrealized Losses	(13)
Corporate Obligations [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	774
Total, Unrealized Losses	(109)
Corporate Obligations [Member] | MBIA [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	135	[2]
Total, Unrealized Losses	(19)	[2]
All Others [Member] | MBIA [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	155	[2]
Total, Unrealized Losses	(14)	[2]
All Others [Member] | All Others [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	86
Total, Unrealized Losses	$ (3)

[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.