Variable Interest Entities (Summary Of Nonconsolidated VIEs Assets And Liabilities) (Detail) - USD ($) $ in Millions		Jun. 30, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Insurance loss recoverable		$ 483	$ 504
Loss and loss adjustment expense reserves		714	541
Global Structured Finance [Member]
Variable Interest Entity [Line Items]
VIE Assets		16,956	20,088
Maximum Exposure to Loss		7,813	10,391
Investments	[1]	27	76
Premiums receivable	[2]	45	55
Insurance loss recoverable	[3]	287	306
Unearned premium revenue	[4]	43	52
Loss and loss adjustment expense reserves	[5]	405	406
Global Structured Finance [Member] | Collateralized Debt Obligations [Member]
Variable Interest Entity [Line Items]
VIE Assets		1,188	3,167
Maximum Exposure to Loss		466	1,914
Investments	[1]	8	51
Premiums receivable	[2]	0	2
Unearned premium revenue	[4]	0	0
Loss and loss adjustment expense reserves	[5]	0	73
Global Structured Finance [Member] | Residential Mortgage Backed Securities [Member]
Variable Interest Entity [Line Items]
VIE Assets		8,067	9,146
Maximum Exposure to Loss		4,182	4,796
Investments	[1]	19	20
Premiums receivable	[2]	25	28
Insurance loss recoverable	[3]	286	304
Unearned premium revenue	[4]	23	27
Loss and loss adjustment expense reserves	[5]	393	325
Global Structured Finance [Member] | Commercial Mortgage Backed Securities [Member]
Variable Interest Entity [Line Items]
VIE Assets		237	257
Maximum Exposure to Loss		120	145
Premiums receivable	[2]	0	0
Unearned premium revenue	[4]	0	0
Global Structured Finance [Member] | Consumer Asset Backed [Member]
Variable Interest Entity [Line Items]
VIE Assets		4,905	4,893
Maximum Exposure to Loss		1,186	1,331
Premiums receivable	[2]	5	7
Insurance loss recoverable	[3]	1	2
Unearned premium revenue	[4]	4	5
Loss and loss adjustment expense reserves	[5]	12	8
Global Structured Finance [Member] | Corporate Asset Backed [Member]
Variable Interest Entity [Line Items]
VIE Assets		2,559	2,625
Maximum Exposure to Loss		1,859	2,205
Investments	[1]	0	5
Premiums receivable	[2]	15	18
Insurance loss recoverable	[3]	0	0
Unearned premium revenue	[4]	16	20
Global Public Finance [Member]
Variable Interest Entity [Line Items]
VIE Assets		19,270	44,306
Maximum Exposure to Loss		3,050	12,051
Premiums receivable	[2]	11	11
Unearned premium revenue	[4]	17	18
Total Insurance [Member]
Variable Interest Entity [Line Items]
VIE Assets		36,226	64,394
Maximum Exposure to Loss		10,863	22,442
Investments	[1]	27	76
Premiums receivable	[2]	56	66
Insurance loss recoverable	[3]	287	306
Unearned premium revenue	[4]	60	70
Loss and loss adjustment expense reserves	[5]	$ 405	$ 406

[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.