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Short Duration Contracts - Claims development - Mortgage (Details) $ in Millions | Dec. 31, 2024 USD ($) claims | Dec. 31, 2023 USD ($) | Dec. 31, 2022 USD ($) | Dec. 31, 2021 USD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($)
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Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Liabilities for losses and loss adjustment expenses, net of reinsurance | $ 21,118 |  |  |  |  |  |  |  |  |
Mortgage |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred losses and allocated loss adjustment expenses, net of reinsurance | 873 |  |  |  |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | 565 |  |  |  |  |  |  |  |  |
All outstanding liabilities before 2012, net of reinsurance | 13 |  |  |  |  |  |  |  |  |
Liabilities for losses and loss adjustment expenses, net of reinsurance | 321 |  |  |  |  |  |  |  |  |
Mortgage | 2015 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred losses and allocated loss adjustment expenses, net of reinsurance | 188 | $ 188 | $ 189 | $ 191 | $ 191 | $ 189 | $ 195 | $ 198 | $ 197 | $ 223
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | 186 | 186 | 185 | 184 | 183 | 180 | 171 | 151 | 92 | $ 16
Total of IBNR liabilities plus expected development on reported claims | $ 0 |  |  |  |  |  |  |  |  |
Cumulative number of paid claims | claims | 4,686 |  |  |  |  |  |  |  |  |
Mortgage | 2016 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred losses and allocated loss adjustment expenses, net of reinsurance | $ 136 | 136 | 137 | 142 | 142 | 141 | 149 | 171 | 184 |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | 134 | 133 | 132 | 132 | 131 | 127 | 113 | 72 | $ 11 |
Total of IBNR liabilities plus expected development on reported claims | $ 0 |  |  |  |  |  |  |  |  |
Cumulative number of paid claims | claims | 3,557 |  |  |  |  |  |  |  |  |
Mortgage | 2017 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred losses and allocated loss adjustment expenses, net of reinsurance | $ 99 | 99 | 102 | 109 | 108 | 107 | 132 | 179 |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | 95 | 93 | 92 | 90 | 87 | 79 | 48 | $ 9 |  |
Total of IBNR liabilities plus expected development on reported claims | $ 0 |  |  |  |  |  |  |  |  |
Cumulative number of paid claims | claims | 2,707 |  |  |  |  |  |  |  |  |
Mortgage | 2018 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred losses and allocated loss adjustment expenses, net of reinsurance | $ 69 | 69 | 72 | 88 | 89 | 96 | 132 |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | 63 | 60 | 59 | 56 | 50 | 31 | $ 4 |  |  |
Total of IBNR liabilities plus expected development on reported claims | $ 0 |  |  |  |  |  |  |  |  |
Cumulative number of paid claims | claims | 1,966 |  |  |  |  |  |  |  |  |
Mortgage | 2019 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred losses and allocated loss adjustment expenses, net of reinsurance | $ 52 | 51 | 63 | 110 | 119 | 108 |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | 42 | 39 | 34 | 29 | 20 | $ 3 |  |  |  |
Total of IBNR liabilities plus expected development on reported claims | $ 0 |  |  |  |  |  |  |  |  |
Cumulative number of paid claims | claims | 1,435 |  |  |  |  |  |  |  |  |
Mortgage | 2020 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred losses and allocated loss adjustment expenses, net of reinsurance | $ 31 | 33 | 78 | 374 | 420 |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | 19 | 13 | 8 | 4 | $ 1 |  |  |  |  |
Total of IBNR liabilities plus expected development on reported claims | $ 0 |  |  |  |  |  |  |  |  |
Cumulative number of paid claims | claims | 835 |  |  |  |  |  |  |  |  |
Mortgage | 2021 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred losses and allocated loss adjustment expenses, net of reinsurance | $ 17 | 20 | 77 | 144 |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | 8 | 5 | 2 | $ 0 |  |  |  |  |  |
Total of IBNR liabilities plus expected development on reported claims | $ 0 |  |  |  |  |  |  |  |  |
Cumulative number of paid claims | claims | 381 |  |  |  |  |  |  |  |  |
Mortgage | 2022 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred losses and allocated loss adjustment expenses, net of reinsurance | $ 30 | 55 | 173 |  |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | 10 | 3 | $ 0 |  |  |  |  |  |  |
Total of IBNR liabilities plus expected development on reported claims | $ 0 |  |  |  |  |  |  |  |  |
Cumulative number of paid claims | claims | 469 |  |  |  |  |  |  |  |  |
Mortgage | 2023 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred losses and allocated loss adjustment expenses, net of reinsurance | $ 71 | 182 |  |  |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | 7 | $ 0 |  |  |  |  |  |  |  |
Total of IBNR liabilities plus expected development on reported claims | $ 0 |  |  |  |  |  |  |  |  |
Cumulative number of paid claims | claims | 366 |  |  |  |  |  |  |  |  |
Mortgage | 2024 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred losses and allocated loss adjustment expenses, net of reinsurance | $ 180 |  |  |  |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | 1 |  |  |  |  |  |  |  |  |
Total of IBNR liabilities plus expected development on reported claims | $ 1 |  |  |  |  |  |  |  |  |
Cumulative number of paid claims | claims | 40 |  |  |  |  |  |  |  |  |

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