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Separate accounts (Fair Value of Assets) (Details) - USD ($) $ in Millions | Sep. 30, 2023 | Dec. 31, 2022
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Fair Value, Separate Account Investment [Line Items] |  |
Separate account assets | $ 5,306 | $ 5,190
Separate Account, Cash and Cash Equivalents |  |
Fair Value, Separate Account Investment [Line Items] |  |
Separate account assets | 88 | 141
Separate Account, equity securities and mutual funds |  |
Fair Value, Separate Account Investment [Line Items] |  |
Separate account assets | 5,129 | 4,960
Separate Account, Non-U.S. Government Treasuries |  |
Fair Value, Separate Account Investment [Line Items] |  |
Separate account assets | $ 89 | $ 89

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