| Line Item | Jun 30, 2026 | Mar 31, 2026 | Jun 30, 2025 | Mar 31, 2025 | Dec 31, 2024 | Sep 30, 2024 | Jun 30, 2024 | Mar 31, 2024 | Dec 31, 2023 | Sep 30, 2023 | Jun 30, 2023 | Mar 31, 2023 | Dec 31, 2022 | Sep 30, 2022 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Revenues: | ||||||||||||||
| Scheduled premiums earned | — | |||||||||||||
| Refunding premiums earned | — | |||||||||||||
| Premiums earned (net of ceded premiums of $-, $-, $-, and $-) | ||||||||||||||
| Net investment income | ||||||||||||||
| Net realized investment gains (losses) | ||||||||||||||
| Net gains (losses) on financial instruments at fair value and foreign exchange | ||||||||||||||
| Fees and reimbursements | ||||||||||||||
| Other net realized gains (losses) | ||||||||||||||
| Total revenues | ||||||||||||||
| YoY growth | -27.0% | -17.2% | ||||||||||||
| Expenses: | ||||||||||||||
| Losses and loss adjustment | ||||||||||||||
| Amortization of deferred acquisition costs | ||||||||||||||
| Interest | ||||||||||||||
| Total expenses | ||||||||||||||
| Income (loss) from continuing operations before income taxes | ||||||||||||||
| Provision (benefit) for income taxes | ||||||||||||||
| Income (loss) from continuing operations | ||||||||||||||
| Income (loss) from discontinued operations, net of income taxes | ||||||||||||||
| Net income (loss) | ||||||||||||||
| % of revenue | -159.3% | -175.0% | ||||||||||||
| Less: Net income (loss) attributable to noncontrolling interests | ||||||||||||||
| Net income (loss) attributable to MBIA Inc. | ||||||||||||||
| Net income (loss) per common share attributable to MBIA Inc. - basic and diluted | ||||||||||||||
| Net income (loss) per common share attributable to MBIA Inc. - basic | ||||||||||||||
| Net income (loss) per common share attributable to MBIA Inc. - diluted |