Financial Guaranty Contracts Accounted for as Credit Derivatives (Details 6) (USD $) In Millions, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012	Sep. 30, 2013		Sep. 30, 2012	Dec. 31, 2012
Credit Derivatives
Estimated net fair value (Pre-Tax)	$ (1,921)			$ (1,921)			$ (1,793)
Estimated Change in Gain/(Loss) (Pre-Tax)	330		(38)	(120)		(388)
100% widening in spreads
Credit Derivatives
Estimated net fair value (Pre-Tax)	(3,885)	[1]		(3,885)	[1]
Estimated Change in Gain/(Loss) (Pre-Tax)				(1,964)	[1]
50% widening in spreads
Credit Derivatives
Estimated net fair value (Pre-Tax)	(2,901)	[1]		(2,901)	[1]
Estimated Change in Gain/(Loss) (Pre-Tax)				(980)	[1]
25% widening in spreads
Credit Derivatives
Estimated net fair value (Pre-Tax)	(2,410)	[1]		(2,410)	[1]
Estimated Change in Gain/(Loss) (Pre-Tax)				(489)	[1]
10% widening in spreads
Credit Derivatives
Estimated net fair value (Pre-Tax)	(2,115)	[1]		(2,115)	[1]
Estimated Change in Gain/(Loss) (Pre-Tax)				(194)	[1]
Base Scenario
Credit Derivatives
Estimated net fair value (Pre-Tax)	(1,921)	[1]		(1,921)	[1]
Estimated Change in Gain/(Loss) (Pre-Tax)				0	[1]
10% narrowing in spreads
Credit Derivatives
Estimated net fair value (Pre-Tax)	(1,770)	[1]		(1,770)	[1]
Estimated Change in Gain/(Loss) (Pre-Tax)				151	[1]
25% narrowing in spreads
Credit Derivatives
Estimated net fair value (Pre-Tax)	(1,544)	[1]		(1,544)	[1]
Estimated Change in Gain/(Loss) (Pre-Tax)				377	[1]
50% narrowing in spreads
Credit Derivatives
Estimated net fair value (Pre-Tax)	(1,168)	[1]		(1,168)	[1]
Estimated Change in Gain/(Loss) (Pre-Tax)				$ 753	[1]

[1] Includes the effects of spreads on both the underlying asset classes and the Company’s own credit spread.