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Investments - Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments |  |  |
Realized gains (losses) on securities | $ 0 | $ (36) | $ (116)
Net of tax |  |  |
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments |  |  |
Realized gains (losses) on securities before impairments | 21 | (20) | (90)
Impairment allowance on securities | (21) | (8) | (2)
Realized gains (losses) on securities | 0 | (28) | (92)
Change in unrealized | 85 | 210 | (633)
Total pretax |  |  |
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments |  |  |
Realized gains (losses) on securities before impairments | 27 | (25) | (113)
Impairment allowance on securities | (27) | (11) | (3)
Realized gains (losses) on securities | 0 | (36) | (116)
Change in unrealized | 108 | 267 | (803)
Fixed maturities |  |  |
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments |  |  |
Realized gains (losses) on securities before impairments | (5) | (35) | (27)
Impairment allowance on fixed maturity securities | (27) | (10) | (3)
Realized gains (losses) on securities | (32) | (45) | (30)
Change in unrealized | 108 | 267 | (803)
Equity securities |  |  |
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments |  |  |
Realized gains (losses) on securities before impairments | 32 | 10 | (96)
Realized gains (losses) on securities | 32 | 10 | (96)
Change in unrealized | 0 | 0 | 0
Mortgage loans and other investments |  |  |
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments |  |  |
Realized gains (losses) on securities before impairments | 0 | 0 | 10
Impairment allowance on mortgage loans and other investments | 0 | (1) | 0
Realized gains (losses) on securities | 0 | (1) | 10
Change in unrealized | 0 | 0 | 0
Total tax effects |  |  |
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments |  |  |
Realized gains (losses) on securities before impairments | (6) | 5 | 23
Impairment allowance on securities | 6 | 3 | 1
Realized gains (losses) on securities | 0 | 8 | 24
Change in unrealized | $ (23) | $ (57) | $ 170

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