Fair Value Measurement - Fair Value of Financial Instruments (Details) - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Assets:
Fixed-maturity securities		$ 10,823	$ 11,023
Short-term investments		590	396
Other invested assets		162	169
Credit derivative assets		13	81
Liabilities:
Credit derivative liabilities		402	446
Other invested assets		93	93
Carrying Amount [Member]
Assets:
Fixed-maturity securities		10,233	10,627
Short-term investments		590	396
Other invested assets	[1]	146	150
Credit derivative assets		13	81
FG VIEs’ assets, at fair value		876	1,261
Other assets		205	206
Liabilities:
Financial guaranty insurance contracts	[2]	3,483	3,998
Long-term debt		1,306	1,300
Credit derivative liabilities		402	446
FG VIEs’ liabilities with recourse, at fair value		807	1,225
FG VIEs’ liabilities without recourse, at fair value		151	124
Other liabilities		12	9
Estimated Fair Value [Member]
Assets:
Fixed-maturity securities		10,233	10,627
Short-term investments		590	396
Other invested assets	[1]	147	152
Credit derivative assets		13	81
FG VIEs’ assets, at fair value		876	1,261
Other assets		205	206
Liabilities:
Financial guaranty insurance contracts	[2]	8,738	8,712
Long-term debt		1,546	1,512
Credit derivative liabilities		402	446
FG VIEs’ liabilities with recourse, at fair value		807	1,225
FG VIEs’ liabilities without recourse, at fair value		151	124
Other liabilities		$ 12	$ 9

[1] Includes investments not carried at fair value with a carrying value of $93 million and $93 million as of December 31, 2016 and December 31, 2015, respectively. Excludes investments carried under the equity method.

[2] 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.