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Investments - Holding gains (losses) on equity securities still held (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Holding Gains (Losses) on Equity Securities Still Held [Line Items] |  |  |
Holding gains (losses) on equity securities | $ 80 | $ 34 | $ (90)
Realized gains (losses) on securities |  |  |
Holding Gains (Losses) on Equity Securities Still Held [Line Items] |  |  |
Holding gains (losses) on equity securities | 24 | (2) | (95)
Net investment income |  |  |
Holding Gains (Losses) on Equity Securities Still Held [Line Items] |  |  |
Holding gains (losses) on equity securities | $ 56 | $ 36 | $ 5

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- Definition Amount of unrealized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + 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)(d)(2)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477250/944-220-S99-1 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 321 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 4 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479536/321-10-50-4 + Details
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