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Separate accounts (Fair value of assets) (Details) - USD ($) $ in Millions | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
--- | --- | --- | ---
Fair Value, Separate Account Investment [Line Items] |  |  |
Separate account assets | $ 5,573 | $ 5,190 | $ 5,560
Separate Account, Cash and Cash Equivalents |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Separate account assets | 65 | 141 | 165
Separate Account, equity securities and mutual funds |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Separate account assets | 5,417 | 4,960 | 5,296
Separate Account, Non-U.S. Government Treasuries |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Separate account assets | $ 91 | $ 89 | $ 99

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