Reinsurance and Other Monoline Exposures - Reinsurance and Other Monoline Exposures (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	$ 71
Ceded Premium, net of Commissions	(92)
Assumed Expected Loss and LAE	(127)
Ceded Expected Loss and LAE	101
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	(8)
Assumed Expected Loss and LAE	0
Ceded Expected Loss and LAE	11
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	(13)
Assumed Expected Loss and LAE	0
Ceded Expected Loss and LAE	46
Radian [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	0
Ceded Premium, net of Commissions	(13)
Assumed Expected Loss and LAE	0
Ceded Expected Loss and LAE	19
Syncora Guarantee Inc. [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	0
Ceded Premium, net of Commissions	(29)
Assumed Expected Loss and LAE	0
Ceded Expected Loss and LAE	4
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 and LAE	0
Ceded Expected Loss and LAE	15
Swiss Reinsurance Co. [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	0
Ceded Premium, net of Commissions	(3)
Assumed Expected Loss and LAE	0
Ceded Expected Loss and LAE	6
Ambac [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	43
Ceded Premium, net of Commissions	0
Assumed Expected Loss and LAE	(19)
Ceded Expected Loss and LAE	0
National Public Finance Guarantee Corporation [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	7
Ceded Premium, net of Commissions	0
Assumed Expected Loss and LAE	(7)
Ceded Expected Loss and LAE	0
MBIA Inc. [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	5
Ceded Premium, net of Commissions	0
Assumed Expected Loss and LAE	(9)
Ceded Expected Loss and LAE	0
FGIC [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	5
Ceded Premium, net of Commissions	0
Assumed Expected Loss and LAE	(3)
Ceded Expected Loss and LAE	0
Ambac Assurance Corp. Segregated account [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	13
Ceded Premium, net of Commissions	0
Assumed Expected Loss and LAE	(83)
Ceded Expected Loss and LAE	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 and LAE	(6)
Ceded Expected Loss and LAE	0
Other [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	(2)
Ceded Premium, net of Commissions	(23)
Assumed Expected Loss and LAE	0
Ceded Expected Loss and LAE	$ 0