Investments (Portion Of Unrealized Gains And Losses On Equity Investments Held) (Detail) - USD ($) $ in Millions |
3 Months Ended | |
|---|---|---|
Mar. 31, 2026 |
Mar. 31, 2025 |
|
| Gain (Loss) on Investments [Line Items] | ||
| Realized investment gains (losses) | $ (0) | $ (5) |
| Equity and Trading securities [Member] | Net gains (losses) recognized during the period on equity and trading securities [Member] | ||
| Gain (Loss) on Investments [Line Items] | ||
| Realized investment gains (losses) | (2) | (3) |
| Equity and Trading securities [Member] | Net gains (losses) recognized during the period on equity and trading securities sold during the period [Member] | ||
| Gain (Loss) on Investments [Line Items] | ||
| Realized investment gains (losses) | 0 | 2 |
| Equity and Trading securities [Member] | Unrealized gains (losses) recognized during the period on equity and trading securities still held at the reporting date [Member] | ||
| Gain (Loss) on Investments [Line Items] | ||
| Realized investment gains (losses) | $ (2) | $ (5) |