Business Segments (Summary Of Company's Segment Results) (Parenthetical) (Detail) - USD ($) $ in Millions |
3 Months Ended | |
|---|---|---|
Mar. 31, 2026 |
Mar. 31, 2025 |
|
| Operating Segments [Member] | U S Public Finance Insurance [Member] | ||
| Segment Reporting Information [Line Items] | ||
| Net investment income | $ 15 | $ 15 |
| Operating Segments [Member] | Corporate Operations [Member] | ||
| Segment Reporting Information [Line Items] | ||
| Net investment income | 6 | 7 |
| Operating Segments [Member] | International And Structured Finance Insurance [Member] | ||
| Segment Reporting Information [Line Items] | ||
| Net investment income | 3 | 3 |
| Intersegment Eliminations [Member] | ||
| Segment Reporting Information [Line Items] | ||
| Net investment income | $ (6) | $ (7) |