Fair Value Measurement - Fair Value of Financial Instruments (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Assets:
Fixed-maturity securities	$ 11,258		$ 10,615
Short-term investments	767		904
Other invested assets	126		170
Credit derivative assets	68		94
Liabilities:
Credit derivative liabilities	963		1,787
Carrying Amount [Member]
Assets:
Fixed-maturity securities	10,491		9,711
Short-term investments	767		904
Other invested assets	108		147
Credit derivative assets	68		94
FG VIEs’ assets, at fair value	1,398		2,565
Other assets	184		179
Liabilities:
Financial guaranty insurance contracts	3,823	[1]	3,783	[1]
Long-term debt	1,303		816
Credit derivative liabilities	963		1,787
FG VIEs’ liabilities with recourse, at fair value	1,277		1,790
FG VIEs’ liabilities without recourse, at fair value	142		1,081
Other liabilities	27		36
Estimated Fair Value [Member]
Assets:
Fixed-maturity securities	10,491		9,711
Short-term investments	767		904
Other invested assets	110		155
Credit derivative assets	68		94
FG VIEs’ assets, at fair value	1,398		2,565
Other assets	184		179
Liabilities:
Financial guaranty insurance contracts	6,205	[1]	5,128	[1]
Long-term debt	1,603		970
Credit derivative liabilities	963		1,787
FG VIEs’ liabilities with recourse, at fair value	1,277		1,790
FG VIEs’ liabilities without recourse, at fair value	142		1,081
Other liabilities	$ 27		$ 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.