Reinsurance and Other Monoline Exposures - Reinsurance and Other Monoline Exposures (Details) $ in Millions	Sep. 30, 2015 USD ($)
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	$ 69
Ceded Premium, net of Commissions	(52)
Assumed Expected Loss to be Paid	(156)
Ceded Expected Loss to be Paid	110
American Overseas Reinsurance Company Limited (f/k/a Ram Re) [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	0
Ceded Premium, net of Commissions	(7)
Assumed Expected Loss to be Paid	0
Ceded Expected Loss to be Paid	25
Tokio Marine & Nichido Fire Insurance Co., Ltd. (“Tokio”) [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	0
Ceded Premium, net of Commissions	(11)
Assumed Expected Loss to be Paid	0
Ceded Expected Loss to be Paid	56
Syncora Guarantee Inc. [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	0
Ceded Premium, net of Commissions	(26)
Assumed Expected Loss to be Paid	0
Ceded Expected Loss to be Paid	6
Mitsui Sumitomo Insurance Co. Ltd. [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	0
Ceded Premium, net of Commissions	(3)
Assumed Expected Loss to be Paid	0
Ceded Expected Loss to be Paid	23
Ambac [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	42
Ceded Premium, net of Commissions	0
Assumed Expected Loss to be Paid	(13)
Ceded Expected Loss to be Paid	0
Ambac Assurance Corp. Segregated account [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	11
Ceded Premium, net of Commissions	0
Assumed Expected Loss to be Paid	(68)
Ceded Expected Loss to be Paid	0
CIFG Assurance North America Inc. [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	0
Ceded Premium, net of Commissions	0
Assumed Expected Loss to be Paid	(48)
Ceded Expected Loss to be Paid	0
MBIA Inc. [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	5
Ceded Premium, net of Commissions	0
Assumed Expected Loss to be Paid	(10)
Ceded Expected Loss to be Paid	0
National Public Finance Guarantee Corporation [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	6
Ceded Premium, net of Commissions	0
Assumed Expected Loss to be Paid	7
Ceded Expected Loss to be Paid	0
Financial Guaranty Insurance Co [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	4
Ceded Premium, net of Commissions	0
Assumed Expected Loss to be Paid	(10)
Ceded Expected Loss to be Paid	0
Other [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	1
Ceded Premium, net of Commissions	(5)
Assumed Expected Loss to be Paid	0
Ceded Expected Loss to be Paid	$ 0