Accumulated Other Comprehensive Income (Details Of The Reclassification From AOCI) (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gains (losses) on financial instruments at fair value and foreign exchange	$ (8)	$ (12)	$ 5	$ (29)
Amounts reclassified from AOCI [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income (loss) attributable to MBIA Inc.	0	0	0	(12)
Unrealized gains (losses) on AFS, net [Member] \| Amounts reclassified from AOCI [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized investment gains (losses)	0	0	0	(7)
Foreign currency translation [Member] \| Amounts reclassified from AOCI [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gains (losses) on financial instruments at fair value and foreign exchange	$ 0	$ 0	$ 0	$ (5)

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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+ Details