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Investments (Portion Of Unrealized Gains And Losses On Equity Investments Held) (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Gain (Loss) on Investments [Line Items] |  |  |
Realized investment gains (losses) | $ (76) | $ (41) | $ 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) | (21) | 6
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 | (6) | 1
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) | $ (15) | $ 5

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