Fair Value Measurement (Details 5) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Assets:
Short-term investments	$ 817		$ 734
Other invested assets	212		223
Credit derivative assets	141		153
FG VIEs' assets, at fair value	2,688		2,819
Liabilities:
Credit derivative liabilities	1,934		1,457
FG VIEs' liabilities with recourse, at fair value	2,090		2,397
FG VIEs' liabilities without recourse, at fair value	1,051		1,061
Carrying Amount
Assets:
Fixed maturity securities	10,056		10,142
Short-term investments	817		734
Other invested assets	177		170
Credit derivative assets	141		153
FG VIEs' assets, at fair value	2,688		2,819
Other assets	166		186
Liabilities:
Financial guaranty insurance contracts	3,918	[1]	4,657	[1]
Long-term debt	836		1,038
Credit derivative liabilities	1,934		1,457
FG VIEs' liabilities with recourse, at fair value	2,090		2,397
FG VIEs' liabilities without recourse, at fair value	1,051		1,061
Other liabilities	47		16
Estimated Fair Value
Assets:
Fixed maturity securities	10,056		10,142
Short-term investments	817		734
Other invested assets	182		182
Credit derivative assets	141		153
FG VIEs' assets, at fair value	2,688		2,819
Other assets	166		186
Liabilities:
Financial guaranty insurance contracts	6,537	[1]	4,313	[1]
Long-term debt	1,091		1,186
Credit derivative liabilities	1,934		1,457
FG VIEs' liabilities with recourse, at fair value	2,090		2,397
FG VIEs' liabilities without recourse, at fair value	1,051		1,061
Other liabilities	$ 47		$ 16

[1] Carrying amount includes the the assets and liabilities related to financial guaranty insurance contract premiums, losses, and salvage and subrogation and other recoverables net of reinsurance.