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Claim, Claim Adjustment Expense and Future Policy Benefit Reserves (Specialty - Surety - Net Strengthening or Releasing of Prior Accident Year Reserves) (Details) - Specialty - 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
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total | $ (73) | $ (69) | $ (92) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Surety |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (76) | (67) | (79) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total net development for accident years prior to 2012 | 3 | (2) | (3) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total unallocated claim adjustment expense development | 0 | 0 | (10) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total | (73) | (69) | (92) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Surety | 2012 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (1) | (1) | (1) | $ (6) | $ (7) | $ (18) | $ (28) | $ (24) | $ 2 |  |  |  |  |  |  |  |  | $ (84)
Surety | 2013 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | 0 | (1) | (4) | (4) | (15) | (9) | (6) | $ 1 |  |  |  |  |  |  |  |  | $ (38) |
Surety | 2014 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (2) | 0 | (15) | (9) | (25) | (30) | $ 1 |  |  |  |  |  |  |  |  | $ (80) |  |
Surety | 2015 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (5) | (5) | (16) | (25) | (27) | $ 0 |  |  |  |  |  |  |  |  | $ (78) |  |  |
Surety | 2016 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (3) | (17) | (25) | (15) | $ 0 |  |  |  |  |  |  |  |  | $ (60) |  |  |  |
Surety | 2017 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (13) | (19) | (12) | $ (5) |  |  |  |  |  |  |  |  | $ (49) |  |  |  |  |
Surety | 2018 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (29) | (17) | $ (6) |  |  |  |  |  |  |  |  | $ (52) |  |  |  |  |  |
Surety | 2019 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (14) | $ (7) |  |  |  |  |  |  |  |  | $ (21) |  |  |  |  |  |  |
Surety | 2020 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | $ (9) |  |  |  |  |  |  |  |  | $ (9) |  |  |  |  |  |  |  |

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