Reinsurance and Other Monoline Exposures (Details 2) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Ceded Par Amount	$ 29,478	[1]
Ceded Par Outstanding	23,661
Assumed Par Outstanding	34,168
Ceded par outstanding related to insured credit derivatives	3,364
Assumed Premium Receivable, net of Commissions	90
Ceded Premium Payable, net of Commissions	(133)
Assumed Expected Loss and LAE	(187)
Ceded Expected Loss and LAE	61
National Public Finance Guarantee Corporation
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Fixed maturity securities wrapped by monoline reinsurer	524
American Overseas Reinsurance Company Limited (f/k/a Ram Re)
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Ceded Par Amount	8,695	[1],[2]
Ceded Par Outstanding	0	[2]
Assumed Par Outstanding	30	[2]
Assumed Premium Receivable, net of Commissions	0
Ceded Premium Payable, net of Commissions	(9)
Assumed Expected Loss and LAE	0
Ceded Expected Loss and LAE	5
Tokio Marine & Nichido Fire Insurance Co., Ltd.
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Ceded Par Amount	7,420	[1]
Ceded Par Outstanding	0
Assumed Par Outstanding	0
Assumed Premium Receivable, net of Commissions	0
Ceded Premium Payable, net of Commissions	(22)
Assumed Expected Loss and LAE	0
Ceded Expected Loss and LAE	33
Radian Asset Assurance Inc.
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Ceded Par Amount	4,781	[1]
Ceded Par Outstanding	38
Assumed Par Outstanding	1,194
Assumed Premium Receivable, net of Commissions	0
Ceded Premium Payable, net of Commissions	(17)
Assumed Expected Loss and LAE	0
Ceded Expected Loss and LAE	12
Syncora Guarantee Inc.
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Ceded Par Amount	4,119	[1]
Ceded Par Outstanding	1,790
Assumed Par Outstanding	162
Assumed Premium Receivable, net of Commissions	0
Ceded Premium Payable, net of Commissions	(39)
Assumed Expected Loss and LAE	22
Ceded Expected Loss and LAE	0
Mitsui Sumitomo Insurance Co. Ltd.
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Ceded Par Amount	2,160	[1],[3]
Ceded Par Outstanding	0	[3]
Assumed Par Outstanding	0	[3]
Assumed Premium Receivable, net of Commissions	0
Ceded Premium Payable, net of Commissions	(4)
Assumed Expected Loss and LAE	0
Ceded Expected Loss and LAE	7
ACA Financial Guaranty Corp.
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Ceded Par Amount	810	[1]
Ceded Par Outstanding	5
Assumed Par Outstanding	10
Swiss Reinsurance Co.
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Ceded Par Amount	401	[1]
Ceded Par Outstanding	0
Assumed Par Outstanding	0
Assumed Premium Receivable, net of Commissions	0
Ceded Premium Payable, net of Commissions	(3)
Assumed Expected Loss and LAE	0
Ceded Expected Loss and LAE	0
Ambac
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Fixed maturity securities wrapped by monoline reinsurer	474
Ceded Par Amount	85	[1]
Ceded Par Outstanding	6,451
Assumed Par Outstanding	18,307
Assumed Premium Receivable, net of Commissions	69
Ceded Premium Payable, net of Commissions	0
Assumed Expected Loss and LAE	(80)
Ceded Expected Loss and LAE	0
CIFG Assurance North America Inc.
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Ceded Par Amount	61	[1]
Ceded Par Outstanding	237
Assumed Par Outstanding	5,201
Assumed Premium Receivable, net of Commissions	0
Ceded Premium Payable, net of Commissions	0
Assumed Expected Loss and LAE	0
Ceded Expected Loss and LAE	4
MBIA Inc.
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Ceded Par Amount	0	[1],[4]
Ceded Par Outstanding	10,549	[4]
Assumed Par Outstanding	7,497	[4]
Assumed Premium Receivable, net of Commissions	14
Ceded Premium Payable, net of Commissions	0
Assumed Expected Loss and LAE	(11)
Ceded Expected Loss and LAE	0
Financial Guaranty Insurance Co.
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Ceded Par Amount	0	[1]
Ceded Par Outstanding	2,535
Assumed Par Outstanding	1,721
Assumed Premium Receivable, net of Commissions	7
Ceded Premium Payable, net of Commissions	0
Assumed Expected Loss and LAE	(118)
Ceded Expected Loss and LAE	0
Other
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Fixed maturity securities wrapped by monoline reinsurer	28
Ceded Par Amount	946	[1]
Ceded Par Outstanding	2,056
Assumed Par Outstanding	46
Assumed Premium Receivable, net of Commissions	0
Ceded Premium Payable, net of Commissions	(39)
Assumed Expected Loss and LAE	0
Ceded Expected Loss and LAE	$ 0

[1] Includes $3,364 million in ceded par outstanding related to insured credit derivatives.

[2] Represents “Withdrawn Rating.”

[3] The Company has structural collateral agreements satisfying the triple-A credit requirement of S&P and/or Moody’s.

[4] MBIA Inc. includes various subsidiaries which are rated A and B by S&P and Baa1, B1 and B3 by Moody’s.