Variable Interest Entities (Summary Of Nonconsolidated VIEs Assets And Liabilities) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Collateralized Debt Obligations [Member]
Variable Interest Entity [Line Items]
VIE Assets	$ 12,688		$ 16,925
Maximum Exposure to Loss	8,769		10,873
Investments			0	[1]
Premiums receivable	57	[2]	62	[2]
Insurance loss recoverable	5	[3]	5	[3]
Unearned premium revenue	50	[4]	55	[4]
Loss and loss adjustment expense reserves	16	[5]	37	[5]
Derivative liabilities	95	[6]	74	[6]
Residential Mortgage Backed Securities [Member]
Variable Interest Entity [Line Items]
VIE Assets	23,812		34,061
Maximum Exposure to Loss	10,294		13,075
Investments			11	[1]
Premiums receivable	59	[2]	77	[2]
Insurance loss recoverable	700	[3]	3,278	[3]
Unearned premium revenue	57	[4]	75	[4]
Loss and loss adjustment expense reserves	351	[5]	440	[5]
Derivative liabilities	6	[6]	4	[6]
Commercial Mortgage Backed Securities [Member]
Variable Interest Entity [Line Items]
VIE Assets	4,628		4,801
Maximum Exposure to Loss	2,284		2,432
Investments			0	[1]
Premiums receivable	1	[2]	2	[2]
Insurance loss recoverable	0	[3]	0	[3]
Unearned premium revenue	1	[4]	2	[4]
Loss and loss adjustment expense reserves	0	[5]	0	[5]
Derivative liabilities	0	[6]	0	[6]
Consumer Asset Backed [Member]
Variable Interest Entity [Line Items]
VIE Assets	5,404		5,820
Maximum Exposure to Loss	2,878		3,086
Investments			10	[1]
Premiums receivable	17	[2]	19	[2]
Insurance loss recoverable	0	[3]	0	[3]
Unearned premium revenue	17	[4]	19	[4]
Loss and loss adjustment expense reserves	19	[5]	21	[5]
Derivative liabilities	0	[6]	0	[6]
Corporate Asset Backed [Member]
Variable Interest Entity [Line Items]
VIE Assets	15,717		19,980
Maximum Exposure to Loss	8,914		9,981
Investments			0	[1]
Premiums receivable	102	[2]	123	[2]
Insurance loss recoverable	19	[3]	13	[3]
Unearned premium revenue	119	[4]	140	[4]
Loss and loss adjustment expense reserves	0	[5]	0	[5]
Derivative liabilities	0	[6]	0	[6]
Global Structured Finance [Member]
Variable Interest Entity [Line Items]
VIE Assets	62,249		81,587
Maximum Exposure to Loss	33,139		39,447
Investments			21	[1]
Premiums receivable	236	[2]	283	[2]
Insurance loss recoverable	724	[3]	3,296	[3]
Unearned premium revenue	244	[4]	291	[4]
Loss and loss adjustment expense reserves	386	[5]	498	[5]
Derivative liabilities	101	[6]	78	[6]
Global Public Finance [Member]
Variable Interest Entity [Line Items]
VIE Assets	44,456		39,259
Maximum Exposure to Loss	19,353		21,346
Investments			0	[1]
Premiums receivable	197	[2]	220	[2]
Insurance loss recoverable	0	[3]	0	[3]
Unearned premium revenue	242	[4]	267	[4]
Loss and loss adjustment expense reserves	5	[5]	4	[5]
Derivative liabilities	0	[6]	0	[6]
Total Insurance [Member]
Variable Interest Entity [Line Items]
VIE Assets	106,705		120,846
Maximum Exposure to Loss	52,492		60,793
Investments			21	[1]
Premiums receivable	433	[2]	503	[2]
Insurance loss recoverable	724	[3]	3,296	[3]
Unearned premium revenue	486	[4]	558	[4]
Loss and loss adjustment expense reserves	391	[5]	502	[5]
Derivative liabilities	$ 101	[6]	$ 78	[6]

[1] Reported within "Investments" on MBIA's consolidated balance sheets.

[2] Reported within "Premiums receivable" on MBIA's consolidated balance sheets.

[3] Reported within "Insurance loss recoverable" on MBIA's consolidated balance sheets.

[4] Reported within "Unearned premium revenue" on MBIA's consolidated balance sheets.

[5] Reported within "Loss and loss adjustment expense reserves" on MBIA's consolidated balance sheets.

[6] Reported within "Derivative liabilities" on MBIA's consolidated balance sheets.