Investments (Securities Held In Unrealized Loss Position And Insured By Financial Guarantor And The Related Insurance Loss Reserve On Company Insured Investments) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	$ 2,092		$ 2,387
Total, Unrealized Losses	(278)		(478)
Mortgage-Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	360
Total, Unrealized Losses	(91)
Asset-Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	330
Total, Unrealized Losses	125
Corporate Obligations [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	495
Total, Unrealized Losses	(37)
Wrapped Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	618
Total, Unrealized Losses	(183)
Loss and Loss Adjustment Expense Reserves	16	[1]
Wrapped Securities [Member] | All Other [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	142
Total, Unrealized Losses	(19)
Wrapped Securities [Member] | Mortgage-Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	241
Total, Unrealized Losses	(77)
Wrapped Securities [Member] | Mortgage-Backed Securities [Member] | MBIA [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	11	[2]
Total, Unrealized Losses	(1)	[2]
Wrapped Securities [Member] | Mortgage-Backed Securities [Member] | All Other [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	230
Total, Unrealized Losses	(76)
Wrapped Securities [Member] | Asset-Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	207
Total, Unrealized Losses	(76)
Loss and Loss Adjustment Expense Reserves	16	[1]
Wrapped Securities [Member] | Asset-Backed Securities [Member] | MBIA [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	149	[2]
Total, Unrealized Losses	(64)	[2]
Loss and Loss Adjustment Expense Reserves	16	[1],[2]
Wrapped Securities [Member] | Asset-Backed Securities [Member] | All Other [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	58
Total, Unrealized Losses	(12)
Wrapped Securities [Member] | Corporate Obligations [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	28
Total, Unrealized Losses	(11)
Wrapped Securities [Member] | Corporate Obligations [Member] | MBIA [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	4	[2]
Wrapped Securities [Member] | Corporate Obligations [Member] | All Other [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	24
Total, Unrealized Losses	(11)
Wrapped Securities [Member] | All Other [Member] | MBIA [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	134	[2]
Total, Unrealized Losses	(19)	[2]
Wrapped Securities [Member] | All Other [Member] | All Other [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	$ 8

[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.