Reinsurance and Other Monoline Exposures - Exposure by Reinsurer (Details) $ in Millions	Jun. 30, 2016 USD ($)
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	$ 13,024	[1]
Second-to- Pay Insured Par Outstanding	13,262	[1]
Assumed Par Outstanding	18,780	[1]
American Overseas Reinsurance Company Limited [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	4,511	[1],[2]
Second-to- Pay Insured Par Outstanding	0	[1],[2]
Assumed Par Outstanding	30	[1],[2]
Tokio Marine & Nichido Fire Insurance Co., Ltd. (“Tokio”) [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	3,887	[1],[2]
Second-to- Pay Insured Par Outstanding	0	[1],[2]
Assumed Par Outstanding	0	[1],[2]
Syncora Guarantee Inc. [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	2,269	[1],[2]
Second-to- Pay Insured Par Outstanding	1,184	[1],[2]
Assumed Par Outstanding	662	[1],[2]
Mitsui Sumitomo Insurance Co. Ltd. [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	1,513	[1],[2]
Second-to- Pay Insured Par Outstanding	0	[1],[2]
Assumed Par Outstanding	0	[1],[2]
Aca Financial Guaranty Corp [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	657	[1]
Second-to- Pay Insured Par Outstanding	33	[1]
Assumed Par Outstanding	0	[1]
Ambac Assurance Corporation [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	115	[1]
Second-to- Pay Insured Par Outstanding	3,541	[1]
Assumed Par Outstanding	8,862	[1]
National [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	0	[1],[3]
Second-to- Pay Insured Par Outstanding	4,967	[1],[3]
Assumed Par Outstanding	4,960	[1],[3]
MBIA [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	0	[1]
Second-to- Pay Insured Par Outstanding	1,357	[1]
Assumed Par Outstanding	414	[1]
FGIC [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	0	[1]
Second-to- Pay Insured Par Outstanding	1,341	[1]
Assumed Par Outstanding	593	[1]
Ambac Assurance Corp. Segregated account [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	0	[1]
Second-to- Pay Insured Par Outstanding	81	[1]
Assumed Par Outstanding	645	[1]
CIFG Assurance North America Inc. [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	0	[1],[4]
Second-to- Pay Insured Par Outstanding	43	[1],[4]
Assumed Par Outstanding	2,488	[1],[4]
Other [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	72	[1],[2]
Second-to- Pay Insured Par Outstanding	715	[1],[2]
Assumed Par Outstanding	126	[1],[2]
Non-affiliated Reinsurers [Member]
Ceded Credit Risk [Line Items]
Funds held under reinsurance agreements	$ 438

[1] Includes par related to insured credit derivatives.

[2] The total collateral posted by all non-affiliated reinsurers required or agreeing to post collateral as of June 30, 2016 was approximately $438 million.

[3] Rated AA+ by KBRA.

[4] On July 1, 2016, AGC acquired all of the issued and outstanding capital stock of CIFG Holding Inc., the parent of financial guaranty insurer CIFG. On July 5, 2016, CIFG merged with and into AGC, with AGC as the surviving company. See Note 2, Acquisitions, for additional information.