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Investments (Portion Of Unrealized Gains And Losses On Equity Investments Held) (Detail) - USD ($) $ in Millions | 3 Months Ended
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Mar. 31, 2025 | Mar. 31, 2024
Gain (Loss) on Investments [Line Items] |  |
Realized investment gains (losses) | $ (5) | $ (1)
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) | 3 | 2
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) | 2 | 0
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) | $ 5 | $ 2

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- Definition Amount of realized gain (loss) on investment. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(3)(a)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477250/944-220-S99-1 + Details
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