Reinsurance and Other Monoline Exposures - Exposure by Reinsurer (Details) $ in Millions	Sep. 30, 2015 USD ($)	[1]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	$ 16,311
Second-to- Pay Insured Par Outstanding	16,522
Assumed Par Outstanding	22,889
American Overseas Reinsurance Company Limited (f/k/a Ram Re) [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	5,480	[2]
Second-to- Pay Insured Par Outstanding	0	[2]
Assumed Par Outstanding	30	[2]
Tokio Marine & Nichido Fire Insurance Co., Ltd. (“Tokio”) [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	4,426	[3]
Second-to- Pay Insured Par Outstanding	0	[3]
Assumed Par Outstanding	0	[3]
Syncora Guarantee Inc. [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	3,505
Second-to- Pay Insured Par Outstanding	1,538
Assumed Par Outstanding	159
Mitsui Sumitomo Insurance Co. Ltd. [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	1,854	[3]
Second-to- Pay Insured Par Outstanding	0	[3]
Assumed Par Outstanding	0	[3]
Aca Financial Guaranty Corp [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	714	[4]
Second-to- Pay Insured Par Outstanding	19	[4]
Assumed Par Outstanding	0	[4]
Ambac [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	117
Second-to- Pay Insured Par Outstanding	4,370
Assumed Par Outstanding	11,633
National Public Finance Guarantee Corporation [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	0
Second-to- Pay Insured Par Outstanding	5,448
Assumed Par Outstanding	5,259
MBIA Inc. [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	0	[5]
Second-to- Pay Insured Par Outstanding	2,584	[5]
Assumed Par Outstanding	449	[5]
Financial Guaranty Insurance Co [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	0
Second-to- Pay Insured Par Outstanding	1,551
Assumed Par Outstanding	674
Ambac Assurance Corp. Segregated account [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	0
Second-to- Pay Insured Par Outstanding	95
Assumed Par Outstanding	888
CIFG Assurance North America Inc. [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	0
Second-to- Pay Insured Par Outstanding	96
Assumed Par Outstanding	3,663
Other [Member]
Ceded Credit Risk [Line Items]
Ceded Par Outstanding	215
Second-to- Pay Insured Par Outstanding	821
Assumed Par Outstanding	$ 134

[1] Includes par related to insured credit derivatives.

[2] Represents “Withdrawn Rating.”

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

[4] Represents “Not Rated.”

[5] MBIA includes subsidiaries MBIA Insurance Corp. rated B by S&P and B2 by Moody's and MBIA U.K. Insurance Ltd. rated B by S&P and Ba2 by Moody’s.