Reinsurance and Other Monoline Exposures - Exposure by Reinsurer (Details) - USD ($) $ in Millions		Dec. 31, 2015		Dec. 31, 2014
Ceded Credit Risk [Line Items]
Ceded Par Outstanding		$ 14,621	[1]	$ 22,975
Second-to- Pay Insured Par Outstanding	[1],[2]	14,608
Assumed Par Outstanding	[1]	21,339
American Overseas Reinsurance Company Limited (f/k/a Ram Re) [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	[1],[3]	5,227
Second-to- Pay Insured Par Outstanding	[1],[3]	0
Assumed Par Outstanding	[1],[3]	30
Tokio Marine & Nichido Fire Insurance Co., Ltd. (“Tokio”) [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	[1],[3],[4]	4,216
Second-to- Pay Insured Par Outstanding	[1],[3],[4]	0
Assumed Par Outstanding	[1],[3],[4]	0
Syncora Guarantee Inc. [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	[1],[3]	2,451
Second-to- Pay Insured Par Outstanding	[1],[2],[3]	1,244
Assumed Par Outstanding	[1],[3]	727
Mitsui Sumitomo Insurance Co. Ltd. [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	[1],[3],[4]	1,818
Second-to- Pay Insured Par Outstanding	[1],[3],[4]	0
Assumed Par Outstanding	[1],[3],[4]	0
Aca Financial Guaranty Corp [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	[1]	714
Second-to- Pay Insured Par Outstanding	[1],[2]	20
Assumed Par Outstanding	[1]	0
Ambac [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	[1]	117
Second-to- Pay Insured Par Outstanding	[1],[2]	3,889
Assumed Par Outstanding	[1]	10,388
National Public Finance Guarantee Corporation [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	[1],[5]	0
Second-to- Pay Insured Par Outstanding	[1],[2],[5]	5,299
Assumed Par Outstanding	[1],[5]	5,100
MBIA Inc. [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	[1],[6]	0
Second-to- Pay Insured Par Outstanding	[1],[2],[6]	1,802
Assumed Par Outstanding	[1],[6]	440
FGIC [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	[1],[7]	0
Second-to- Pay Insured Par Outstanding	[1],[2],[7]	1,424
Assumed Par Outstanding	[1],[7]	652
Ambac Assurance Corp. Segregated account [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	[1]	0
Second-to- Pay Insured Par Outstanding	[1],[2]	91
Assumed Par Outstanding	[1]	873
CIFG Assurance North America Inc. [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	[1]	0
Second-to- Pay Insured Par Outstanding	[1],[2]	43
Assumed Par Outstanding	[1]	2,996
Other [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	[1],[8]	78
Second-to- Pay Insured Par Outstanding	[1],[2],[8]	796
Assumed Par Outstanding	[1],[8]	$ 133

[1] Includes par related to insured credit derivatives

[2] Assured Guaranty’s internal rating.

[3] Positive ceded premiums written were due to commutations and changes in expected Debt Service schedules.

[4] The Company benefits from trust arrangements that satisfy the triple-A credit requirement of S&P and/or Moody’s.

[5] National is rated AA+ by KBRA.

[6] MBIA includes subsidiaries MBIA Insurance Corp. rated B by S&P and B3 by Moody's and MBIA U.K. Insurance Ltd. rated BB by S&P and Ba2 by Moody’s.

[7] FGIC includes subsidiaries Financial Guaranty Insurance Company and FGIC UK Limited both of which had their ratings withdrawn by rating agencies.

[8] The total collateral posted by all non-affiliated reinsurers required or agreeing to post collateral as of December 31, 2015, is approximately $470 million.