Variable Interest Entities (Summary Of Nonconsolidated VIEs Assets And Liabilities) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Collateralized Debt Obligations [Member]
Variable Interest Entity [Line Items]
VIE Assets	$ 16,925		$ 26,507
Maximum Exposure to Loss	10,873		15,466
Investments			42	[1]
Premiums receivable	62	[2]	67	[2]
Insurance loss recoverable	5	[3]
Unearned Premium Revenue	55	[4]	58	[4]
Loss and loss adjustment expense reserves	37	[5]	3	[5]
Derivative liabilities	74	[6]	113	[6]
Residential Mortgage-Backed Securities [Member]
Variable Interest Entity [Line Items]
VIE Assets	34,061		47,669
Maximum Exposure to Loss	13,075		16,379
Investments	11	[1]	25	[1]
Premiums receivable	77	[2]	87	[2]
Insurance loss recoverable	3,278	[3]	2,773	[3]
Unearned Premium Revenue	75	[4]	86	[4]
Loss and loss adjustment expense reserves	440	[5]	428	[5]
Derivative liabilities	4	[6]	5	[6]
Commercial Mortgage-Backed [Member]
Variable Interest Entity [Line Items]
VIE Assets	4,801		5,001
Maximum Exposure to Loss	2,432		2,644
Premiums receivable	2	[2]	2	[2]
Unearned Premium Revenue	2	[4]	2	[4]
Consumer Asset-Backed [Member]
Variable Interest Entity [Line Items]
VIE Assets	5,820		8,015
Maximum Exposure to Loss	3,086		4,563
Investments	10	[1]	16	[1]
Premiums receivable	19	[2]	26	[2]
Unearned Premium Revenue	19	[4]	25	[4]
Loss and loss adjustment expense reserves	21	[5]	23	[5]
Corporate Asset-Backed [Member]
Variable Interest Entity [Line Items]
VIE Assets	19,980		29,855
Maximum Exposure to Loss	9,981		15,577
Investments			241	[1]
Premiums receivable	123	[2]	192	[2]
Insurance loss recoverable	13	[3]	22	[3]
Unearned Premium Revenue	140	[4]	205	[4]
Derivative liabilities			1	[6]
Global Structured Finance [Member]
Variable Interest Entity [Line Items]
VIE Assets	81,587		117,047
Maximum Exposure to Loss	39,447		54,629
Investments	21	[1]	324	[1]
Premiums receivable	283	[2]	374	[2]
Insurance loss recoverable	3,296	[3]	2,795	[3]
Unearned Premium Revenue	291	[4]	376	[4]
Loss and loss adjustment expense reserves	498	[5]	454	[5]
Derivative liabilities	78	[6]	119	[6]
Global Public Finance [Member]
Variable Interest Entity [Line Items]
VIE Assets	39,259		42,106
Maximum Exposure to Loss	21,346		21,774
Premiums receivable	220	[2]	215	[2]
Unearned Premium Revenue	267	[4]	270	[4]
Loss and loss adjustment expense reserves	4	[5]
Total Insurance [Member]
Variable Interest Entity [Line Items]
VIE Assets	120,846		159,153
Maximum Exposure to Loss	60,793		76,403
Investments	21	[1]	324	[1]
Premiums receivable	503	[2]	589	[2]
Insurance loss recoverable	3,296	[3]	2,795	[3]
Unearned Premium Revenue	558	[4]	646	[4]
Loss and loss adjustment expense reserves	502	[5]	454	[5]
Derivative liabilities	$ 78	[6]	$ 119	[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.