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Claim and Claim Adjustment Expense Reserves and Future Policy Benefit Reserves (Commercial - Workers' Compensation - Net Strengthening or Releasing of Prior Accident Year Reserves) (Details) - Commercial - USD ($) $ in Millions | 12 Months Ended | 24 Months Ended | 36 Months Ended | 48 Months Ended | 60 Months Ended | 72 Months Ended | 84 Months Ended | 96 Months Ended | 108 Months Ended | 120 Months Ended
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2022 | Dec. 31, 2022 | Dec. 31, 2022 | Dec. 31, 2022 | Dec. 31, 2022 | Dec. 31, 2022 | Dec. 31, 2022 | Dec. 31, 2022 | Dec. 31, 2022
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total | $ (152) | $ (82) | $ (96) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Workers' Compensation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (110) | (50) | (80) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Adjustment for development on a discounted basis | (3) | 2 | 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total net development for accident years prior to 2013 | (49) | (34) | (18) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total unallocated claim adjustment expense development | 10 | 0 | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total | (152) | (82) | (96) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Workers' Compensation | 2013 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (11) | (4) | (9) | $ (21) | $ (11) | $ (25) | $ 26 | $ 20 | $ 35 |  |  |  |  |  |  |  |  | $ 0
Workers' Compensation | 2014 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (18) | 9 | (7) | (4) | (2) | (27) | (1) | $ 13 |  |  |  |  |  |  |  |  | $ (37) |
Workers' Compensation | 2015 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (19) | (10) | (12) | (14) | 2 | (25) | $ 9 |  |  |  |  |  |  |  |  | $ (69) |  |
Workers' Compensation | 2016 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (24) | (11) | (16) | (14) | (9) | $ (21) |  |  |  |  |  |  |  |  | $ (95) |  |  |
Workers' Compensation | 2017 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (3) | 2 | (21) | (11) | $ (8) |  |  |  |  |  |  |  |  | $ (41) |  |  |  |
Workers' Compensation | 2018 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | 0 | (13) | (12) | $ (10) |  |  |  |  |  |  |  |  | $ (35) |  |  |  |  |
Workers' Compensation | 2019 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (1) | (12) | $ (3) |  |  |  |  |  |  |  |  | $ (16) |  |  |  |  |  |
Workers' Compensation | 2020 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (20) | $ (11) |  |  |  |  |  |  |  |  | $ (31) |  |  |  |  |  |  |
Workers' Compensation | 2021 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | $ (14) |  |  |  |  |  |  |  |  | $ (14) |  |  |  |  |  |  |  |

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