Investments (Portion Of Unrealized Gains And Losses On Equity Investments Held) (Detail) - USD ($) $ in Millions |
3 Months Ended | |
|---|---|---|
Mar. 31, 2023 |
Mar. 31, 2022 |
|
| Gain (Loss) on Investments [Line Items] | ||
| Realized investment gains (losses) | $ (3) | $ (3) |
| Equity and Trading securities [Member] | Net gains and (losses) recognized during the period on equity and trading securities [Member] | ||
| Gain (Loss) on Investments [Line Items] | ||
| Realized investment gains (losses) | 1 | (10) |
| Equity and Trading securities [Member] | Net gains and (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 | 1 |
| Equity and Trading securities [Member] | Unrealized gains and (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) | $ 1 | $ (11) |