Fair Value Measurement - Fair Value of Financial Instruments (Details) - USD ($) $ in Millions		Jun. 30, 2015	Dec. 31, 2014
Assets:
Fixed-maturity securities		$ 11,416	$ 11,258
Short-term investments		834	767
Other invested assets		215	126
Credit derivative assets		81	68
Liabilities:
Credit derivative liabilities		1,007	963
Carrying Amount [Member]
Assets:
Fixed-maturity securities		10,582	10,491
Short-term investments		834	767
Other invested assets		180	108
Credit derivative assets		81	68
FG VIEs’ assets, at fair value		1,596	1,398
Other assets		219	184
Liabilities:
Financial guaranty insurance contracts	[1]	4,247	3,823
Long-term debt		1,305	1,303
Credit derivative liabilities		1,007	963
FG VIEs’ liabilities with recourse, at fair value		1,361	1,277
FG VIEs’ liabilities without recourse, at fair value		171	142
Other liabilities		152	27
Estimated Fair Value [Member]
Assets:
Fixed-maturity securities		10,582	10,491
Short-term investments		834	767
Other invested assets		182	110
Credit derivative assets		81	68
FG VIEs’ assets, at fair value		1,596	1,398
Other assets		219	184
Liabilities:
Financial guaranty insurance contracts	[1]	8,275	6,205
Long-term debt		1,486	1,603
Credit derivative liabilities		1,007	963
FG VIEs’ liabilities with recourse, at fair value		1,361	1,277
FG VIEs’ liabilities without recourse, at fair value		171	142
Other liabilities		$ 152	$ 27

[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.