Schedule II - (Notes to Condensed Financial Statements) (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Long-term debt principal amount purchased	$ 308
Fair value of securities pledged as collateral	282	$ 313
Securities posted as collateral to derivative counterparties	$ 214	181
MBIA Inc. Senior Notes [Member]
Long-term debt, interest rate	5.70%
Long-term debt, maturity year	2034
Mbia Inc. Debentures [Member]
Long-term debt principal amount purchased	$ 13
Long-term debt, interest rate	7.00%
Long-term debt, maturity year	2025
6.400% Senior Notes due 2022 [Member]
Long-term debt principal amount purchased	$ 115	150
Long-term debt principal amount purchased, par value	100.00%
Long-term debt, interest rate	6.40%
Long-term debt, maturity year	2022
National Public Finance Guarantee Holdings, Inc. [Member]
Dividends from subsidiaries		1	$ 108
MBIA Inc. [Member]
Liquid assets	$ 294
Fair value of securities pledged as collateral	282	313
Securities posted as collateral to derivative counterparties	214	181
National [Member]
Dividends from subsidiaries	81	$ 134
National [Member] \| Mbia Inc. Debentures [Member]
Long-term debt principal amount purchased	10
MBIA Capital Corp. [Member]
Dividends from subsidiaries	$ 3

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