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Schedule II - (Notes to Condensed Financial Statements) (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Condensed Financial Statements, Captions [Line Items]
Long-term debt principal amount purchased	$ 308
Dividend declared per common share		$ 8
O 2023 Q4 Dividends [Member]
Condensed Financial Statements, Captions [Line Items]
Dividend payment date	Dec. 22, 2023
Mbia Inc. Debentures [Member]
Condensed Financial Statements, Captions [Line Items]
Long-term debt, interest rate	7.00%
Long-term debt, maturity year	2025
MBIA Inc. Senior Notes [Member]
Condensed Financial Statements, Captions [Line Items]
Long-term debt, interest rate	5.70%
Long-term debt, maturity year	2034
6.625% Senior Notes due 2028 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt Instrument, Face Amount	$ 29
Long-term debt, interest rate	6.625%
Long-term debt, maturity year	2028
7.150% Senior Notes due 2027 [Member]
Condensed Financial Statements, Captions [Line Items]
Long-term debt, interest rate	7.15%
Long-term debt, maturity year	2027
MBIA Corp Surplus Notes [Member] | Mbia Inc. Debentures [Member]
Condensed Financial Statements, Captions [Line Items]
Long-term debt principal amount purchased	$ 13
MBIA Inc. [Member]
Condensed Financial Statements, Captions [Line Items]
Liquid assets	380
Fair value of securities pledged as collateral	$ 213	$ 241
Dividend declared per common share		$ 8
MBIA Inc. [Member] | O 2023 Q4 Dividends [Member]
Condensed Financial Statements, Captions [Line Items]
Dividend payment date	Dec. 22, 2023
National [Member]
Condensed Financial Statements, Captions [Line Items]
Dividends from subsidiaries	$ 69		$ 72
National [Member] | S 2023 A Dividends [Member]
Condensed Financial Statements, Captions [Line Items]
Dividends from subsidiaries		$ 550
National [Member] | O 2023 A Right Dividends [Member]
Condensed Financial Statements, Captions [Line Items]
Dividends from subsidiaries		$ 97
National [Member] | 7.00% Senior Notes due 2025 [Member]
Condensed Financial Statements, Captions [Line Items]
Long-term debt principal amount purchased	10
MBIA Corp [Member] | 7.150% Senior Notes due 2027 [Member]
Condensed Financial Statements, Captions [Line Items]
Long-term debt principal amount purchased	5
MBIA Corp [Member] | 7.00% Senior Notes due 2025 [Member]
Condensed Financial Statements, Captions [Line Items]
Long-term debt principal amount purchased	$ 1

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Number 210
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-Section S99
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