Reinsurance and Other Monoline Exposures (Details 2) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Ceded Par Amount	$ 30,929	[1]
Ceded Par Outstanding	24,461
Assumed Par Outstanding	36,761
Ceded par outstanding related to insured credit derivatives	3,720
Assumed Premium Receivable, net of Commissions	81
Ceded Premium Payable, net of Commissions	(145)
Assumed Expected Loss and LAE	(104)
Ceded Expected Loss and LAE	46
National Public Finance Guarantee Corporation
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Fixed maturity securities wrapped by monoline reinsurer	596
American Overseas Reinsurance Company Limited [Member]
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Ceded Par Amount	5,002	[1]
Ceded Par Outstanding	42
Assumed Par Outstanding	1,331
Assumed Premium Receivable, net of Commissions	0
Ceded Premium Payable, net of Commissions	(19)
Assumed Expected Loss and LAE	0
Ceded Expected Loss and LAE	(4)
Tokio Marine and Nichido Fire Insurance Co Ltd [Member]
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Ceded Par Amount	7,938	[1],[2]
Ceded Par Outstanding	0	[2]
Assumed Par Outstanding	0	[2]
Assumed Premium Receivable, net of Commissions	0
Ceded Premium Payable, net of Commissions	(25)
Assumed Expected Loss and LAE	0
Ceded Expected Loss and LAE	30
Radian Asset Assurance Inc [Member]
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Ceded Par Amount	9,387	[1],[3]
Ceded Par Outstanding	0	[3]
Assumed Par Outstanding	24	[3]
Assumed Premium Receivable, net of Commissions	0
Ceded Premium Payable, net of Commissions	(11)
Assumed Expected Loss and LAE	0
Ceded Expected Loss and LAE	6
Syncora Guarantee Inc [Member]
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Ceded Par Amount	4,001	[1]
Ceded Par Outstanding	1,886
Assumed Par Outstanding	162
Assumed Premium Receivable, net of Commissions	0
Ceded Premium Payable, net of Commissions	(40)
Assumed Expected Loss and LAE	19
Ceded Expected Loss and LAE	1
Mitsui Sumitomo Insurance Co Ltd [Member]
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Ceded Par Amount	2,213	[1],[2]
Ceded Par Outstanding	0	[2]
Assumed Par Outstanding	0	[2]
Assumed Premium Receivable, net of Commissions	0
Ceded Premium Payable, net of Commissions	(5)
Assumed Expected Loss and LAE	0
Ceded Expected Loss and LAE	7
Aca Financial Guaranty Corp [Member]
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Ceded Par Amount	819	[1]
Ceded Par Outstanding	6
Assumed Par Outstanding	1
Swiss Reinsurance Co [Member]
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Ceded Par Amount	426	[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	2
Ambac
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Fixed maturity securities wrapped by monoline reinsurer	499
Ceded Par Amount	85	[1]
Ceded Par Outstanding	6,669
Assumed Par Outstanding	20,040
Assumed Premium Receivable, net of Commissions	73
Ceded Premium Payable, net of Commissions	0
Assumed Expected Loss and LAE	(71)
Ceded Expected Loss and LAE	0
CIFG Assurance North America Inc. [Member]
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Ceded Par Amount	61	[1]
Ceded Par Outstanding	255
Assumed Par Outstanding	5,392
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	10,616	[4]
Assumed Par Outstanding	7,834	[4]
Assumed Premium Receivable, net of Commissions	0
Ceded Premium Payable, net of Commissions	0
Assumed Expected Loss and LAE	(17)
Ceded Expected Loss and LAE	0
Financial Guaranty Insurance Co [Member]
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Ceded Par Amount	0	[1]
Ceded Par Outstanding	3,052
Assumed Par Outstanding	1,932
Assumed Premium Receivable, net of Commissions	8
Ceded Premium Payable, net of Commissions	0
Assumed Expected Loss and LAE	(35)
Ceded Expected Loss and LAE	0
Other
Exposure, Premium Receivable, and Loss and LAE by Reinsurer
Fixed maturity securities wrapped by monoline reinsurer	30
Ceded Par Amount	997	[1]
Ceded Par Outstanding	1,935
Assumed Par Outstanding	45
Assumed Premium Receivable, net of Commissions	0
Ceded Premium Payable, net of Commissions	(42)
Assumed Expected Loss and LAE	0
Ceded Expected Loss and LAE	$ 0

[1] Includes $3,720 million in ceded par outstanding related to insured credit derivatives.

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

[3] Represents “Withdrawn Rating.”

[4] MBIA Inc. includes various subsidiaries which are rated BB, CCC, WR by S&P and Caa2, B3, Baa2, WR and NR by Moody’s.