Financial Guaranty Contracts Accounted for as Credit Derivatives (Details 6) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012	Dec. 31, 2012
Credit Derivatives
Estimated net fair value (Pre-Tax)	$ (2,393)			$ (1,793)
Net unrealized gains (losses) on credit derivatives	(610)		(634)
100% widening in spreads
Credit Derivatives
Estimated net fair value (Pre-Tax)	(4,859)	[1]
Net unrealized gains (losses) on credit derivatives	(2,466)	[1]
50% widening in spreads
Credit Derivatives
Estimated net fair value (Pre-Tax)	(3,626)	[1]
Net unrealized gains (losses) on credit derivatives	(1,233)	[1]
25% widening in spreads
Credit Derivatives
Estimated net fair value (Pre-Tax)	(3,010)	[1]
Net unrealized gains (losses) on credit derivatives	(617)	[1]
10% widening in spreads
Credit Derivatives
Estimated net fair value (Pre-Tax)	(2,640)	[1]
Net unrealized gains (losses) on credit derivatives	(247)	[1]
Base Scenario
Credit Derivatives
Estimated net fair value (Pre-Tax)	(2,393)	[1]
Net unrealized gains (losses) on credit derivatives	0	[1]
10% narrowing in spreads
Credit Derivatives
Estimated net fair value (Pre-Tax)	(2,169)	[1]
Net unrealized gains (losses) on credit derivatives	224	[1]
25% narrowing in spreads
Credit Derivatives
Estimated net fair value (Pre-Tax)	(1,837)	[1]
Net unrealized gains (losses) on credit derivatives	556	[1]
50% narrowing in spreads
Credit Derivatives
Estimated net fair value (Pre-Tax)	(1,285)	[1]
Net unrealized gains (losses) on credit derivatives	$ 1,108	[1]

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