Earnings Per Share (Computation Of Basic And Diluted Earnings Per Share) (Detail) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Basic and diluted earnings per share:
Net income (loss) from continuing operations available to common shareholders - Basic		$ (185)	$ (35)	$ (346)	$ (144)
Income (loss) from discontinued operations, net of income taxes		(1)	1	(2)	1
Less: Net income (loss) from discontinued operations attributable to noncontrolling interests		(1)	0	5	0
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent		0	1	(7)	1
Net Income (Loss) Attributable to Parent		$ (185)	$ (34)	$ (353)	$ (143)
Basic weighted average shares	[1]	47,009,765	49,878,191	48,654,638	49,779,681
Diluted weighted average shares	[1]	47,009,765	49,878,191	48,654,638	49,779,681
Continuing operations - Basic		$ (3.93)	$ (0.68)	$ (7.1)	$ (2.88)
Continuing operations - Diluted		(3.93)	(0.68)	(7.1)	(2.88)
Discontinued operations - Basic		(0.01)	0.01	(0.15)	0.01
Discontinued operations - Diluted		(0.01)	0.01	(0.15)	0.01
Net income (loss) per share attributable to MBIA Inc. - basic		(3.94)	(0.67)	(7.25)	(2.87)
Earnings Per Share, Diluted		$ (3.94)	$ (0.67)	$ (7.25)	$ (2.87)
Potentially dilutive securities excluded from the calculation of diluted EPS because of antidilutive affect		4.3	5	4.3	5

[1] Includes approximately 1 million of participating securities that met the service condition and were eligible to receive nonforfeitable dividends or dividend equivalents for the three and nine months ended September 30, 2023 and 2022.