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Claim, Claim Adjustment Expense 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, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2021 | Dec. 31, 2021 | Dec. 31, 2021 | Dec. 31, 2021 | Dec. 31, 2021 | Dec. 31, 2021 | Dec. 31, 2021 | Dec. 31, 2021 | Dec. 31, 2021
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total | $ (82) | $ (96) | $ (13) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Workers' Compensation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (49) | (85) | (77) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Adjustment for development on a discounted basis | 2 | 2 | 3 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total net development for accident years prior to 2012 | (35) | (13) | 38 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total unallocated claim adjustment expense development | 0 | 0 | 23 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total | (82) | (96) | (13) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Workers' Compensation | 2012 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | 1 | (5) | (3) | $ (2) | $ (5) | $ 9 | $ 10 | $ 32 | $ 26 |  |  |  |  |  |  |  |  | $ 63
Workers' Compensation | 2013 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (4) | (9) | (21) | (11) | (25) | 26 | 20 | $ 35 |  |  |  |  |  |  |  |  | $ 11 |
Workers' Compensation | 2014 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | 9 | (7) | (4) | (2) | (27) | (1) | $ 13 |  |  |  |  |  |  |  |  | $ (19) |  |
Workers' Compensation | 2015 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (10) | (12) | (14) | 2 | (25) | $ 9 |  |  |  |  |  |  |  |  | $ (50) |  |  |
Workers' Compensation | 2016 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (11) | (16) | (14) | (9) | $ (21) |  |  |  |  |  |  |  |  | $ (71) |  |  |  |
Workers' Compensation | 2017 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | 2 | (21) | (11) | $ (8) |  |  |  |  |  |  |  |  | $ (38) |  |  |  |  |
Workers' Compensation | 2018 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (13) | (12) | $ (10) |  |  |  |  |  |  |  |  | $ (35) |  |  |  |  |  |
Workers' Compensation | 2019 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (12) | $ (3) |  |  |  |  |  |  |  |  | $ (15) |  |  |  |  |  |  |
Workers' Compensation | 2020 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | $ (11) |  |  |  |  |  |  |  |  | $ (11) |  |  |  |  |  |  |  |

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