Fair Value Measurement - Fair Value of Financial Instruments (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Assets:
Short-term investments	$ 837		$ 904
Other invested assets	127		170
Credit derivative assets	86		94
FG VIEs' assets, at fair value	1,296		2,565
Liabilities:
Credit derivative liabilities	1,654		1,787
FG VIEs' liabilities with recourse, at fair value	1,326		1,790
FG VIEs' liabilities without recourse, at fair value	133		1,081
Carrying Amount
Assets:
Fixed maturity securities	10,485		9,711
Short-term investments	837		904
Other invested assets	108		147
Credit derivative assets	86		94
FG VIEs' assets, at fair value	1,296		2,565
Other assets	213		179
Liabilities:
Financial guaranty insurance contracts	3,586	[1]	3,783	[1]
Long-term debt	1,303		816
Credit derivative liabilities	1,654		1,787
FG VIEs' liabilities with recourse, at fair value	1,326		1,790
FG VIEs' liabilities without recourse, at fair value	133		1,081
Other liabilities	107		36
Estimated Fair Value
Assets:
Fixed maturity securities	10,485		9,711
Short-term investments	837		904
Other invested assets	111		155
Credit derivative assets	86		94
FG VIEs' assets, at fair value	1,296		2,565
Other assets	213		179
Liabilities:
Financial guaranty insurance contracts	6,147	[1]	5,128	[1]
Long-term debt	1,579		970
Credit derivative liabilities	1,654		1,787
FG VIEs' liabilities with recourse, at fair value	1,326		1,790
FG VIEs' liabilities without recourse, at fair value	133		1,081
Other liabilities	$ 107		$ 36

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