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Business Segments - (Summary Of Company's Segment Results) (Parenthetical) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Operating Segments [Member] | U S Public Finance Insurance [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Net investment income | $ 67 | $ 93 | $ 81
Operating Segments [Member] | Corporate Operations [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Net investment income | 30 | 25 | 22
Operating Segments [Member] | International And Structured Finance Insurance [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Net investment income | 11 | 23 | 17
Intersegment Eliminations [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Net investment income | $ (24) | $ (25) | $ (25)

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