Fair Value Measurement (Details 5) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Assets:
Short-term investments	$ 564		$ 734
Other invested assets	205		223
Credit Risk Derivative Assets, at Fair Value	450		469
FG VIEs' assets, at fair value	2,693		2,819
Liabilities:
Credit Risk Derivative Liabilities, at Fair Value	2,151		1,773
FG VIEs' liabilities with recourse, at fair value	2,169		2,397
FG VIEs' liabilities without recourse, at fair value	1,018		1,061
Carrying Amount
Assets:
Fixed maturity securities	10,318		10,142
Short-term investments	564		734
Other invested assets	165		170
Credit Risk Derivative Assets, at Fair Value	450		469
FG VIEs' assets, at fair value	2,693		2,819
Other assets	183		186
Liabilities:
Financial guaranty insurance contracts	4,102	[1]	4,657	[1]
Long-term debt	840	[2]	1,038	[2]
Credit Risk Derivative Liabilities, at Fair Value	2,151		1,773
FG VIEs' liabilities with recourse, at fair value	2,169		2,397
FG VIEs' liabilities without recourse, at fair value	1,018		1,061
Other liabilities	64		16
Estimated Fair Value
Assets:
Fixed maturity securities	10,318		10,142
Short-term investments	564		734
Other invested assets	176		182
Credit Risk Derivative Assets, at Fair Value	450		469
FG VIEs' assets, at fair value	2,693		2,819
Other assets	183		186
Liabilities:
Financial guaranty insurance contracts	6,929	[1]	4,313	[1]
Long-term debt	1,058	[2]	1,186	[2]
Credit Risk Derivative Liabilities, at Fair Value	2,151		1,773
FG VIEs' liabilities with recourse, at fair value	2,169		2,397
FG VIEs' liabilities without recourse, at fair value	1,018		1,061
Other liabilities	$ 64		$ 16

[1] Carrying amount includes the balance sheet amounts related to financial guaranty insurance contract premiums and losses, net of reinsurance.

[2] Carrying amount represented principal less accumulated discount or plus accumulated premium.