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Investments - Fair Values and Unrealized Losses by Investment Category and by Duration of Securities' Continuous Unrealized Loss Position (Details) - USD ($) $ in Millions | Jun. 30, 2025 | Dec. 31, 2024
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Investments, Unrealized Loss Position |  |
Investments, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months | $ 5,007 | $ 6,683
Investments, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 116 | 121
Investments, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer | 5,363 | 5,823
Investments, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 466 | 510
Investments, Available-for-Sale, Unrealized Loss Position | 10,370 | 12,506
Investments, Available-for-Sale, Unrealized Loss Position, Accumulated Loss | 582 | 631
Short-term investments, available-for-sale, continuous unrealized loss position, less than 12 months | 100 | 100
Short-term Investments, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 0 | 0
Short-term investments, available-for-sale, continuous unrealized loss position, 12 months or longer | 0 | 0
Short-term investments, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss | 0 | 0
Short-term investments, available-for-sale, unrealized loss position, total | 100 | 100
Short-term investments, available-for-sale, unrealized loss position, accumulated loss | 0 | 0
Less than 12 months Fair Value | 4,907 | 6,583
Less than 12 Months, Unrealized Loss | 116 | 121
12 months or more, Fair Value | 5,363 | 5,823
12 months or longer, Unrealized Loss | 466 | 510
Total Fair Value | 10,270 | 12,406
Total Unrealized Losses | 582 | 631
Corporate |  |
Investments, Unrealized Loss Position |  |
Less than 12 months Fair Value | 1,738 | 2,815
Less than 12 Months, Unrealized Loss | 51 | 78
12 months or more, Fair Value | 3,037 | 3,634
12 months or longer, Unrealized Loss | 205 | 255
Total Fair Value | 4,775 | 6,449
Total Unrealized Losses | 256 | 333
States, municipalities and political subdivisions |  |
Investments, Unrealized Loss Position |  |
Less than 12 months Fair Value | 1,505 | 1,513
Less than 12 Months, Unrealized Loss | 49 | 25
12 months or more, Fair Value | 2,062 | 1,898
12 months or longer, Unrealized Loss | 255 | 245
Total Fair Value | 3,567 | 3,411
Total Unrealized Losses | 304 | 270
Government-sponsored enterprises |  |
Investments, Unrealized Loss Position |  |
Less than 12 months Fair Value | 1,427 | 1,876
Less than 12 Months, Unrealized Loss | 9 | 8
12 months or more, Fair Value | 124 | 92
12 months or longer, Unrealized Loss | 0 | 1
Total Fair Value | 1,551 | 1,968
Total Unrealized Losses | 9 | 9
Asset-backed |  |
Investments, Unrealized Loss Position |  |
Less than 12 months Fair Value | 237 | 331
Less than 12 Months, Unrealized Loss | 7 | 10
12 months or more, Fair Value | 78 | 96
12 months or longer, Unrealized Loss | 5 | 7
Total Fair Value | 315 | 427
Total Unrealized Losses | 12 | 17
United States government |  |
Investments, Unrealized Loss Position |  |
Less than 12 months Fair Value | 0 | 48
Less than 12 Months, Unrealized Loss | 0 | 0
12 months or more, Fair Value | 62 | 100
12 months or longer, Unrealized Loss | 1 | 2
Total Fair Value | 62 | 148
Total Unrealized Losses | 1 | 2
Foreign government |  |
Investments, Unrealized Loss Position |  |
Less than 12 months Fair Value | 0 | 0
Less than 12 Months, Unrealized Loss | 0 | 0
12 months or more, Fair Value | 0 | 3
12 months or longer, Unrealized Loss | 0 | 0
Total Fair Value | 0 | 3
Total Unrealized Losses | $ 0 | $ 0

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