Consolidated Statements Of Changes In Shareholders' Equity (Unaudited) - USD ($) $ in Millions	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]	Total Shareholders' Equity Of MBIA Inc. [Member]	Preferred Stock [Member]
Total equity balance at Dec. 31, 2018		$ 284	$ 3,025	$ 966	$ (156)	$ (3,000)	$ 1,119
Balance (in common stock shares) at Dec. 31, 2018		283,625,689
Balance (in treasury stock shares) at Dec. 31, 2018						(193,803,976)
Balance (in preferred stock shares) at Dec. 31, 2018								1,315
ASU 2016-13 transition adjustment | ASU 2016-13 [Member]				0
Net income (loss)	$ (145)			(145)
Other comprehensive income (loss)	142				142
Treasury shares acquired under share repurchase program						$ (93)
Treasury shares acquired under share repurchase program (in shares)						(10,273,891)
Other						$ 40
Others (in shares)						920,108
Period change			(28)				(84)
Total equity balance at Sep. 30, 2019	1,048	$ 284	2,997	821	(14)	$ (3,053)	1,035	$ 13
Balance (in treasury stock shares) at Sep. 30, 2019						(203,157,759)
Total equity balance at Jun. 30, 2019			2,995	738	37	$ (3,014)	1,040
Balance (in common stock shares) at Jun. 30, 2019		283,625,689
Balance (in treasury stock shares) at Jun. 30, 2019						(198,824,693)
Balance (in preferred stock shares) at Jun. 30, 2019								1,315
ASU 2016-13 transition adjustment | ASU 2016-13 [Member]				0
Net income (loss)	83			83
Other comprehensive income (loss)	(51)				(51)
Treasury shares acquired under share repurchase program						$ (39)
Treasury shares acquired under share repurchase program (in shares)						(4,341,232)
Other						$ 0
Others (in shares)						8,166
Period change			2				(5)
Total equity balance at Sep. 30, 2019	1,048	$ 284	2,997	821	(14)	$ (3,053)	1,035	$ 13
Balance (in treasury stock shares) at Sep. 30, 2019						(203,157,759)
Total equity balance at Dec. 31, 2019	$ 839		2,999	607	(2)	$ (3,061)	826
Balance (in common stock shares) at Dec. 31, 2019	283,433,401
Balance (in treasury stock shares) at Dec. 31, 2019	(204,000,108)					(204,000,108)
Balance (in preferred stock shares) at Dec. 31, 2019	0							1,315
ASU 2016-13 transition adjustment | ASU 2016-13 [Member]				(42)
Net income (loss)	$ (497)			(497)
Other comprehensive income (loss)	132				132
Treasury shares acquired under share repurchase program						$ (198)
Treasury shares acquired under share repurchase program (in shares)						(26,430,768)
Other						$ 48
Others (in shares)						924,913
Period change			(39)				(596)
Total equity balance at Sep. 30, 2020	$ 243	$ 283	2,960	68	130	$ (3,211)	230	$ 13
Balance (in common stock shares) at Sep. 30, 2020	283,433,401	283,433,401
Balance (in treasury stock shares) at Sep. 30, 2020	(229,505,963)					(229,505,963)
Total equity balance at Jun. 30, 2020			2,959	126	129	$ (3,149)	348
Balance (in treasury stock shares) at Jun. 30, 2020						(220,924,081)
Balance (in preferred stock shares) at Jun. 30, 2020								1,315
ASU 2016-13 transition adjustment | ASU 2016-13 [Member]				0
Net income (loss)	$ (58)			(58)
Other comprehensive income (loss)	1				1
Treasury shares acquired under share repurchase program						$ (62)
Treasury shares acquired under share repurchase program (in shares)						(8,582,686)
Other						$ 0
Others (in shares)						804
Period change			1				(118)
Total equity balance at Sep. 30, 2020	$ 243	$ 283	$ 2,960	$ 68	$ 130	$ (3,211)	$ 230	$ 13
Balance (in common stock shares) at Sep. 30, 2020	283,433,401	283,433,401
Balance (in treasury stock shares) at Sep. 30, 2020	(229,505,963)					(229,505,963)