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Claim, Claim Adjustment Expense and Future Policy Benefit Reserves (Net Prior Year Development) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Segment Reporting Information [Line Items] |  |  |
Pretax (favorable) unfavorable premium development, excluding Life & Group | $ 11 | $ (20) | $ (73)
Specialty |  |  |
Segment Reporting Information [Line Items] |  |  |
Pretax (favorable) unfavorable premium development, excluding Life & Group | (45) | (61) | (92)
Commercial |  |  |
Segment Reporting Information [Line Items] |  |  |
Pretax (favorable) unfavorable premium development, excluding Life & Group | (6) | (7) | (40)
International |  |  |
Segment Reporting Information [Line Items] |  |  |
Pretax (favorable) unfavorable premium development, excluding Life & Group | 2 | (2) | 21
Corporate & Other |  |  |
Segment Reporting Information [Line Items] |  |  |
Pretax (favorable) unfavorable premium development, excluding Life & Group | $ 60 | $ 50 | $ 38

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