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Insurance Regulations And Dividends (Narrative) (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Insurance Regulations And Dividends [Line Items] |  |  |
Percentage of policyholders' surplus | 10.00% |  |
Percentage of adjusted net investment income | 100.00% |  |
Policyholders Surplus [Member] | Minimum [Member] |  |  |
Insurance Regulations And Dividends [Line Items] |  |  |
Policyholders' surplus | $ 65 |  |
MBIA Corp [Member] |  |  |
Insurance Regulations And Dividends [Line Items] |  |  |
Unassigned surplus | 1,900 | $ 1,900 |
Statutory net loss | 28 |  | $ 129
Statutory capital | 152 | 169 |
Policyholders' surplus | 147 |  |
Contingency reserves | 5 |  |
Statutory net income |  | 46 |
National [Member] |  |  |
Insurance Regulations And Dividends [Line Items] |  |  |
Dividends from subsidiaries |  | 72 | 60
Statutory net loss | 142 |  |
Statutory capital | 1,100 | 1,900 |
Policyholders' surplus | 800 |  |
Contingency reserves | 354 |  |
Statutory net income |  | $ 75 | $ 55
National [Member] | Special Dividend [Member] |  |  |
Insurance Regulations And Dividends [Line Items] |  |  |
Dividends from subsidiaries | 550 |  |
National [Member] | Right Dividend [Member] |  |  |
Insurance Regulations And Dividends [Line Items] |  |  |
Dividends from subsidiaries | $ 97 |  |

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- Definition This element represents disclosure of the aggregate cash dividends paid to the entity by consolidated subsidiaries. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 235 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-04(b)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480678/235-10-S99-3 + Details
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