Reinsurance and Other Monoline Exposures - Reinsurance and Other Monoline Exposures (Details) $ in Millions	Mar. 31, 2016 USD ($)
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	$ 79
Ceded Premium, net of Commissions	(53)
Assumed Expected Loss to be Paid	(141)
Ceded Expected Loss to be Paid	92
American Overseas Reinsurance Company Limited [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	0
Ceded Premium, net of Commissions	(6)
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	44
Syncora Guarantee Inc. [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	15
Ceded Premium, net of Commissions	(21)
Assumed Expected Loss to be Paid	0
Ceded Expected Loss to be Paid	5
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	18
Ambac Assurance Corporation [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	39
Ceded Premium, net of Commissions	0
Assumed Expected Loss to be Paid	(3)
Ceded Expected Loss to be Paid	0
Ambac Assurance Corp. Segregated account [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	10
Ceded Premium, net of Commissions	0
Assumed Expected Loss to be Paid	(46)
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	(63)
Ceded Expected Loss to be Paid	0
MBIA [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 [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	6
Ceded Premium, net of Commissions	0
Assumed Expected Loss to be Paid	(4)
Ceded Expected Loss to be Paid	0
FGIC [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	4
Ceded Premium, net of Commissions	0
Assumed Expected Loss to be Paid	(15)
Ceded Expected Loss to be Paid	0
Other [Member]
Ceded Credit Risk [Line Items]
Assumed Premium, net of Commissions	0
Ceded Premium, net of Commissions	(12)
Assumed Expected Loss to be Paid	0
Ceded Expected Loss to be Paid	$ 0