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Claim and Claim Adjustment Expense Reserves and Future Policy Benefit Reserves (Specialty - Surety - Net Incurred Claims and Allocated Claim Adjustment Expenses) (Details) - Surety - Specialty $ in Millions | Dec. 31, 2022 USD ($) claim | Dec. 31, 2021 USD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($) | Dec. 31, 2013 USD ($)
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Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 801 |  |  |  |  |  |  |  |  |
IBNR | 351 |  |  |  |  |  |  |  |  |
2013 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | 82 | $ 82 | $ 82 | $ 83 | $ 87 | $ 91 | $ 106 | $ 115 | $ 121 | $ 120
IBNR | $ 2 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 5,092 |  |  |  |  |  |  |  |  |
2014 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 42 | 43 | 45 | 45 | 60 | 69 | 94 | 124 | $ 123 |
IBNR | $ 3 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 5,127 |  |  |  |  |  |  |  |  |
2015 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 45 | 53 | 58 | 63 | 79 | 104 | 131 | $ 131 |  |
IBNR | $ 1 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 5,074 |  |  |  |  |  |  |  |  |
2016 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 58 | 64 | 67 | 84 | 109 | 124 | $ 124 |  |  |
IBNR | $ 5 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 5,544 |  |  |  |  |  |  |  |  |
2017 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 66 | 71 | 84 | 103 | 115 | $ 120 |  |  |  |
IBNR | $ 4 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 5,855 |  |  |  |  |  |  |  |  |
2018 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 56 | 62 | 91 | 108 | $ 114 |  |  |  |  |
IBNR | $ 16 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 6,196 |  |  |  |  |  |  |  |  |
2019 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 87 | 98 | 112 | $ 119 |  |  |  |  |  |
IBNR | $ 21 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 6,033 |  |  |  |  |  |  |  |  |
2020 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 81 | 119 | $ 128 |  |  |  |  |  |  |
IBNR | $ 51 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 4,452 |  |  |  |  |  |  |  |  |
2021 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 129 | $ 137 |  |  |  |  |  |  |  |
IBNR | $ 105 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 4,168 |  |  |  |  |  |  |  |  |
2022 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 155 |  |  |  |  |  |  |  |  |
IBNR | $ 143 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 2,772 |  |  |  |  |  |  |  |  |

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