Financial Guaranty Contracts Accounted for as Credit Derivatives (Details 6) (USD $)	3 Months Ended			6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011	Jun. 30, 2012		Jun. 30, 2011	Dec. 31, 2011
Credit Derivatives
Estimated net fair value (Pre-Tax)	$ (1,666,000,000)			$ (1,666,000,000)			$ (1,303,900,000)
Unrealized Gains (Losses)	283,327,000		(54,059,000)	(350,431,000)		(325,695,000)
100% widening in spreads
Credit Derivatives
Estimated net fair value (Pre-Tax)	(3,462,100,000)	[1]		(3,462,100,000)	[1]
Unrealized Gains (Losses)				(1,796,100,000)	[1]
50% widening in spreads
Credit Derivatives
Estimated net fair value (Pre-Tax)	(2,564,000,000)	[1]		(2,564,000,000)	[1]
Unrealized Gains (Losses)				(898,000,000)	[1]
25% widening in spreads
Credit Derivatives
Estimated net fair value (Pre-Tax)	(2,114,900,000)	[1]		(2,114,900,000)	[1]
Unrealized Gains (Losses)				(448,900,000)	[1]
10% widening in spreads
Credit Derivatives
Estimated net fair value (Pre-Tax)	(1,845,400,000)	[1]		(1,845,400,000)	[1]
Unrealized Gains (Losses)				(179,400,000)	[1]
Base Scenario
Credit Derivatives
Estimated net fair value (Pre-Tax)	(1,666,000,000)	[1]		(1,666,000,000)	[1]
Unrealized Gains (Losses)				0	[1]
10% narrowing in spreads
Credit Derivatives
Estimated net fair value (Pre-Tax)	(1,509,200,000)	[1]		(1,509,200,000)	[1]
Unrealized Gains (Losses)				156,800,000	[1]
25% narrowing in spreads
Credit Derivatives
Estimated net fair value (Pre-Tax)	(1,275,000,000)	[1]		(1,275,000,000)	[1]
Unrealized Gains (Losses)				391,000,000	[1]
50% narrowing in spreads
Credit Derivatives
Estimated net fair value (Pre-Tax)	(893,600,000)	[1]		(893,600,000)	[1]
Unrealized Gains (Losses)				$ 772,400,000	[1]

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