Variable Interest Entities (Summary Of Nonconsolidated VIEs Assets And Liabilities) (Detail) - USD ($) $ in Millions		Sep. 30, 2016	Dec. 31, 2015
Global Structured Finance [Member]
Variable Interest Entity [Line Items]
VIE Assets		$ 22,195	$ 28,311
Maximum Exposure to Loss		11,252	14,495
Investments	[1]	75	74
Premiums receivable	[2]	59	80
Insurance loss recoverable	[3]	348	418
Unearned premium revenue	[4]	57	78
Loss and loss adjustment expense reserves	[5]	404	418
Derivative liabilities	[6]	1	6
Global Structured Finance [Member] | Collateralized Debt Obligations [Member]
Variable Interest Entity [Line Items]
VIE Assets		3,487	5,712
Maximum Exposure to Loss		2,095	3,046
Investments	[1]	49	51
Premiums receivable	[2]	3	9
Unearned premium revenue	[4]	1	6
Loss and loss adjustment expense reserves	[5]	58	108
Derivative liabilities	[6]	1	6
Global Structured Finance [Member] | Residential Mortgage Backed Securities [Member]
Variable Interest Entity [Line Items]
VIE Assets		9,857	11,524
Maximum Exposure to Loss		5,085	6,072
Investments	[1]	22	23
Premiums receivable	[2]	28	31
Insurance loss recoverable	[3]	347	416
Unearned premium revenue	[4]	27	30
Loss and loss adjustment expense reserves	[5]	339	306
Global Structured Finance [Member] | Commercial Mortgage Backed Securities [Member]
Variable Interest Entity [Line Items]
VIE Assets		270	319
Maximum Exposure to Loss		158	219
Premiums receivable	[2]	0	1
Unearned premium revenue	[4]	0	1
Global Structured Finance [Member] | Consumer Asset Backed [Member]
Variable Interest Entity [Line Items]
VIE Assets		5,021	5,538
Maximum Exposure to Loss		1,397	1,712
Premiums receivable	[2]	7	13
Insurance loss recoverable	[3]	1
Unearned premium revenue	[4]	6	11
Loss and loss adjustment expense reserves	[5]	7	4
Global Structured Finance [Member] | Corporate Asset Backed [Member]
Variable Interest Entity [Line Items]
VIE Assets		3,560	5,218
Maximum Exposure to Loss		2,517	3,446
Investments	[1]	4
Premiums receivable	[2]	21	26
Insurance loss recoverable	[3]	0	2
Unearned premium revenue	[4]	23	30
Global Public Finance [Member]
Variable Interest Entity [Line Items]
VIE Assets		44,313	44,162
Maximum Exposure to Loss		12,802	14,579
Premiums receivable	[2]	143	160
Unearned premium revenue	[4]	161	186
Total Insurance [Member]
Variable Interest Entity [Line Items]
VIE Assets		66,508	72,473
Maximum Exposure to Loss		24,054	29,074
Investments	[1]	75	74
Premiums receivable	[2]	202	240
Insurance loss recoverable	[3]	348	418
Unearned premium revenue	[4]	218	264
Loss and loss adjustment expense reserves	[5]	404	418
Derivative liabilities	[6]	$ 1	$ 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.