Business Segments (Summary Of Company's Segment Results) (Parenthetical) (Detail) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2025 |
Jun. 30, 2024 |
Jun. 30, 2025 |
Jun. 30, 2024 |
|
| Operating Segments [Member] | U S Public Finance Insurance [Member] | ||||
| Segment Reporting Information [Line Items] | ||||
| Net investment income | $ 15 | $ 17 | $ 30 | $ 35 |
| Operating Segments [Member] | Corporate Operations [Member] | ||||
| Segment Reporting Information [Line Items] | ||||
| Net investment income | 6 | 8 | 13 | 16 |
| Operating Segments [Member] | International And Structured Finance Insurance [Member] | ||||
| Segment Reporting Information [Line Items] | ||||
| Net investment income | 3 | 2 | 6 | 5 |
| Intersegment Eliminations [Member] | ||||
| Segment Reporting Information [Line Items] | ||||
| Net investment income | $ (5) | $ (5) | $ (12) | $ (11) |