Variable Interest Entities (Summary Of Nonconsolidated VIEs Assets And Liabilities) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Variable Interest Entity [Line Items]
Insurance loss recoverable	$ 527		$ 533
Global Structured Finance [Member]
Variable Interest Entity [Line Items]
VIE Assets	33,879		35,940
Maximum Exposure to Loss	18,461		19,958
Investments	107	[1]	119	[1]
Premiums receivable	113	[2]	123	[2]
Insurance loss recoverable	519		524	[3]
Unearned premium revenue	112	[4]	121	[4]
Loss and loss adjustment expense reserves	396	[5]	389	[5]
Derivative liabilities	85	[6]	102	[6]
Global Structured Finance [Member] | Collateralized Debt Obligations [Member]
Variable Interest Entity [Line Items]
VIE Assets	7,491		8,613
Maximum Exposure to Loss	4,788		5,623
Investments	95	[1]	110	[1]
Premiums receivable	21	[2]	24	[2]
Unearned premium revenue	17	[4]	20	[4]
Loss and loss adjustment expense reserves	71	[5]	70	[5]
Derivative liabilities	85	[6]	102	[6]
Global Structured Finance [Member] | Residential Mortgage Backed Securities [Member]
Variable Interest Entity [Line Items]
VIE Assets	13,575		14,136
Maximum Exposure to Loss	7,173		7,459
Investments	12	[1]	9	[1]
Premiums receivable	39	[2]	41	[2]
Insurance loss recoverable	513	[3]	518	[3]
Unearned premium revenue	37	[4]	39	[4]
Loss and loss adjustment expense reserves	315	[5]	307	[5]
Global Structured Finance [Member] | Commercial Mortgage Backed Securities [Member]
Variable Interest Entity [Line Items]
VIE Assets	554		571
Maximum Exposure to Loss	265		279
Premiums receivable	1	[2]	1	[2]
Unearned premium revenue	1	[4]	1	[4]
Global Structured Finance [Member] | Consumer Asset Backed [Member]
Variable Interest Entity [Line Items]
VIE Assets	5,856		6,008
Maximum Exposure to Loss	1,916		1,989
Premiums receivable	15	[2]	16	[2]
Unearned premium revenue	14	[4]	14	[4]
Loss and loss adjustment expense reserves	10	[5]	12	[5]
Global Structured Finance [Member] | Corporate Asset Backed [Member]
Variable Interest Entity [Line Items]
VIE Assets	6,403		6,612
Maximum Exposure to Loss	4,319		4,608
Premiums receivable	37	[2]	41	[2]
Insurance loss recoverable	6	[3]	6	[3]
Unearned premium revenue	43	[4]	47	[4]
Global Public Finance [Member]
Variable Interest Entity [Line Items]
VIE Assets	45,700		49,686
Maximum Exposure to Loss	15,595		16,698
Premiums receivable	166	[2]	179	[2]
Unearned premium revenue	200	[4]	211	[4]
Total Insurance [Member]
Variable Interest Entity [Line Items]
VIE Assets	79,579		85,626
Maximum Exposure to Loss	34,056		36,656
Investments	107	[1]	119	[1]
Premiums receivable	279	[2]	302	[2]
Insurance loss recoverable	519	[3]	524	[3]
Unearned premium revenue	312	[4]	332	[4]
Loss and loss adjustment expense reserves	396	[5]	389	[5]
Derivative liabilities	$ 85	[6]	$ 102	[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.