Variable Interest Entities (Summary Of Nonconsolidated VIEs Assets And Liabilities) (Detail) - USD ($) $ in Millions		Sep. 30, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Insurance loss recoverable		$ 611	$ 504
Loss and loss adjustment expense reserves		818	541
Global Structured Finance [Member]
Variable Interest Entity [Line Items]
VIE Assets		15,306	20,088
Maximum Exposure to Loss		6,912	10,391
Investments	[1]	19	76
Premiums receivable	[2]	42	55
Insurance loss recoverable	[3]	250	306
Unearned premium revenue	[4]	41	52
Loss and loss adjustment expense reserves	[5]	418	406
Global Structured Finance [Member] | Collateralized Debt Obligations [Member]
Variable Interest Entity [Line Items]
VIE Assets		0	3,167
Maximum Exposure to Loss		0	1,914
Investments	[1]	0	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		7,660	9,146
Maximum Exposure to Loss		3,955	4,796
Investments	[1]	19	20
Premiums receivable	[2]	24	28
Insurance loss recoverable	[3]	248	304
Unearned premium revenue	[4]	22	27
Loss and loss adjustment expense reserves	[5]	407	325
Global Structured Finance [Member] | Commercial Mortgage Backed Securities [Member]
Variable Interest Entity [Line Items]
VIE Assets		226	257
Maximum Exposure to Loss		106	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		4,939	4,893
Maximum Exposure to Loss		1,107	1,331
Premiums receivable	[2]	5	7
Insurance loss recoverable	[3]	2	2
Unearned premium revenue	[4]	4	5
Loss and loss adjustment expense reserves	[5]	11	8
Global Structured Finance [Member] | Corporate Asset Backed [Member]
Variable Interest Entity [Line Items]
VIE Assets		2,481	2,625
Maximum Exposure to Loss		1,744	2,205
Investments	[1]	0	5
Premiums receivable	[2]	13	18
Insurance loss recoverable	[3]	0	0
Unearned premium revenue	[4]	15	20
Global Public Finance [Member]
Variable Interest Entity [Line Items]
VIE Assets		19,850	44,306
Maximum Exposure to Loss		3,104	12,051
Premiums receivable	[2]	10	11
Unearned premium revenue	[4]	15	18
Total Insurance [Member]
Variable Interest Entity [Line Items]
VIE Assets		35,156	64,394
Maximum Exposure to Loss		10,016	22,442
Investments	[1]	19	76
Premiums receivable	[2]	52	66
Insurance loss recoverable	[3]	250	306
Unearned premium revenue	[4]	56	70
Loss and loss adjustment expense reserves	[5]	$ 418	$ 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.