Variable Interest Entities (Summary Of Nonconsolidated VIEs Assets And Liabilities) (Detail) - USD ($) $ in Millions		Jun. 30, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Maximum Exposure to Loss		$ 6,189	$ 7,284
Investments [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	[1]	16	17
Premiums Receivable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	[2]	35	40
Insurance Loss Recoverable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	[3]	962	987
Unearned Premium Revenue [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	[4]	35	41
Loss And Loss Adjustment Expense Reserves Member [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	[5]	436	357
Global Structured Finance [Member]
Variable Interest Entity [Line Items]
Maximum Exposure to Loss		4,020	5,053
Global Structured Finance [Member] | Investments [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	[1]	16	17
Global Structured Finance [Member] | Premiums Receivable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	[2]	27	31
Global Structured Finance [Member] | Insurance Loss Recoverable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	[3]	962	987
Global Structured Finance [Member] | Unearned Premium Revenue [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	[4]	25	29
Global Structured Finance [Member] | Loss And Loss Adjustment Expense Reserves Member [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	[5]	436	357
Global Structured Finance [Member] | Residential Mortgage Backed Securities [Member]
Variable Interest Entity [Line Items]
Maximum Exposure to Loss		2,441	3,103
Global Structured Finance [Member] | Residential Mortgage Backed Securities [Member] | Investments [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	[1]	16	17
Global Structured Finance [Member] | Residential Mortgage Backed Securities [Member] | Premiums Receivable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	[2]	17	19
Global Structured Finance [Member] | Residential Mortgage Backed Securities [Member] | Insurance Loss Recoverable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	[3]	98	128
Global Structured Finance [Member] | Residential Mortgage Backed Securities [Member] | Unearned Premium Revenue [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	[4]	15	17
Global Structured Finance [Member] | Residential Mortgage Backed Securities [Member] | Loss And Loss Adjustment Expense Reserves Member [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	[5]	426	345
Global Structured Finance [Member] | Commercial Mortgage Backed Securities [Member]
Variable Interest Entity [Line Items]
Maximum Exposure to Loss		38	52
Global Structured Finance [Member] | Commercial Mortgage Backed Securities [Member] | Investments [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	[1]	0	0
Global Structured Finance [Member] | Commercial Mortgage Backed Securities [Member] | Premiums Receivable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	[2]	0	0
Global Structured Finance [Member] | Commercial Mortgage Backed Securities [Member] | Insurance Loss Recoverable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	[3]	0	0
Global Structured Finance [Member] | Commercial Mortgage Backed Securities [Member] | Unearned Premium Revenue [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	[4]	0	0
Global Structured Finance [Member] | Commercial Mortgage Backed Securities [Member] | Loss And Loss Adjustment Expense Reserves Member [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	[5]	0	0
Global Structured Finance [Member] | Consumer Asset Backed [Member]
Variable Interest Entity [Line Items]
Maximum Exposure to Loss		427	560
Global Structured Finance [Member] | Consumer Asset Backed [Member] | Investments [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	[1]	0	0
Global Structured Finance [Member] | Consumer Asset Backed [Member] | Premiums Receivable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	[2]	2	3
Global Structured Finance [Member] | Consumer Asset Backed [Member] | Insurance Loss Recoverable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	[3]	2	1
Global Structured Finance [Member] | Consumer Asset Backed [Member] | Unearned Premium Revenue [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	[4]	1	2
Global Structured Finance [Member] | Consumer Asset Backed [Member] | Loss And Loss Adjustment Expense Reserves Member [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	[5]	10	12
Global Structured Finance [Member] | Corporate Asset Backed [Member]
Variable Interest Entity [Line Items]
Maximum Exposure to Loss		1,114	1,338
Global Structured Finance [Member] | Corporate Asset Backed [Member] | Investments [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	[1]	0	0
Global Structured Finance [Member] | Corporate Asset Backed [Member] | Premiums Receivable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	[2]	8	9
Global Structured Finance [Member] | Corporate Asset Backed [Member] | Insurance Loss Recoverable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	[3]	862	858
Global Structured Finance [Member] | Corporate Asset Backed [Member] | Unearned Premium Revenue [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	[4]	9	10
Global Structured Finance [Member] | Corporate Asset Backed [Member] | Loss And Loss Adjustment Expense Reserves Member [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	[5]	0	0
Global Public Finance [Member]
Variable Interest Entity [Line Items]
Maximum Exposure to Loss		2,169	2,231
Global Public Finance [Member] | Investments [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	[1]	0	0
Global Public Finance [Member] | Premiums Receivable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	[2]	8	9
Global Public Finance [Member] | Insurance Loss Recoverable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	[3]	0	0
Global Public Finance [Member] | Unearned Premium Revenue [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	[4]	10	12
Global Public Finance [Member] | Loss And Loss Adjustment Expense Reserves Member [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	[5]	$ 0	$ 0

[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.