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Investments (Portion Of Unrealized Gains And Losses On Equity Investments Held) (Detail) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
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Jun. 30, 2025 | Jun. 30, 2024 | Jun. 30, 2025 | Jun. 30, 2024
Gain (Loss) on Investments [Line Items] |  |  |  |
Realized investment gains (losses) |  |  | $ (6) | $ (3)
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) | $ 4 | $ (56) | 1 | (58)
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 | 1 | 2 | 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) | $ 4 | $ (57) | $ (1) | $ (59)

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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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