Fair Value Measurement - Fair Value of Financial Instruments (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Assets:
Short-term investments	$ 720		$ 904
Other invested assets	134		170
Credit derivative assets	78		94
FG VIEs' assets, at fair value	1,257		2,565
Liabilities:
Credit derivative liabilities	2,001		1,787
FG VIEs' liabilities with recourse, at fair value	1,346		1,790
FG VIEs' liabilities without recourse, at fair value	101		1,081
Carrying Amount
Assets:
Fixed maturity securities	10,094		9,711
Short-term investments	720		904
Other invested assets	113		147
Credit derivative assets	78		94
FG VIEs' assets, at fair value	1,257		2,565
Other assets	181		179
Liabilities:
Financial guaranty insurance contracts	3,693	[1]	3,783	[1]
Long-term debt	812		816
Credit derivative liabilities	2,001		1,787
FG VIEs' liabilities with recourse, at fair value	1,346		1,790
FG VIEs' liabilities without recourse, at fair value	101		1,081
Other liabilities	62		36
Estimated Fair Value
Assets:
Fixed maturity securities	10,094		9,711
Short-term investments	720		904
Other invested assets	116		155
Credit derivative assets	78		94
FG VIEs' assets, at fair value	1,257		2,565
Other assets	181		179
Liabilities:
Financial guaranty insurance contracts	5,644	[1]	5,128	[1]
Long-term debt	1,050		970
Credit derivative liabilities	2,001		1,787
FG VIEs' liabilities with recourse, at fair value	1,346		1,790
FG VIEs' liabilities without recourse, at fair value	101		1,081
Other liabilities	$ 62		$ 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.