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Investment Information - Aging of available for sale securities in an unrealized loss position (Details) - USD ($) $ in Millions | Sep. 30, 2024 | Dec. 31, 2023
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Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract] |  |
Estimated Fair Value - Less than 12 Months | $ 5,283 | $ 3,867
Estimated Fair Value - 12 Months or More | 6,386 | 9,555
Estimated Fair Value | 11,669 | 13,422
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Gross Unrealized Losses - Less than 12 Months | (102) | (67)
Gross Unrealized Losses - 12 Months or More | (431) | (760)
Gross Unrealized Losses | (533) | (827)
Fixed maturities |  |
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract] |  |
Estimated Fair Value - Less than 12 Months | 4,921 | 3,565
Estimated Fair Value - 12 Months or More | 6,386 | 9,555
Estimated Fair Value | 11,307 | 13,120
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Gross Unrealized Losses - Less than 12 Months | (100) | (65)
Gross Unrealized Losses - 12 Months or More | (431) | (760)
Gross Unrealized Losses | (531) | (825)
Corporate bonds |  |
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract] |  |
Estimated Fair Value - Less than 12 Months | 1,903 | 1,559
Estimated Fair Value - 12 Months or More | 3,316 | 4,959
Estimated Fair Value | 5,219 | 6,518
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Gross Unrealized Losses - Less than 12 Months | (76) | (45)
Gross Unrealized Losses - 12 Months or More | (218) | (419)
Gross Unrealized Losses | (294) | (464)
U.S. government and government agencies |  |
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract] |  |
Estimated Fair Value - Less than 12 Months | 1,815 | 1,066
Estimated Fair Value - 12 Months or More | 571 | 941
Estimated Fair Value | 2,386 | 2,007
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Gross Unrealized Losses - Less than 12 Months | (10) | (10)
Gross Unrealized Losses - 12 Months or More | (38) | (76)
Gross Unrealized Losses | (48) | (86)
Non-U.S. government securities |  |
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract] |  |
Estimated Fair Value - Less than 12 Months | 614 | 365
Estimated Fair Value - 12 Months or More | 743 | 897
Estimated Fair Value | 1,357 | 1,262
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Gross Unrealized Losses - Less than 12 Months | (8) | (4)
Gross Unrealized Losses - 12 Months or More | (76) | (96)
Gross Unrealized Losses | (84) | (100)
Residential mortgage backed securities |  |
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract] |  |
Estimated Fair Value - Less than 12 Months | 213 | 221
Estimated Fair Value - 12 Months or More | 485 | 522
Estimated Fair Value | 698 | 743
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Gross Unrealized Losses - Less than 12 Months | (2) | (3)
Gross Unrealized Losses - 12 Months or More | (48) | (63)
Gross Unrealized Losses | (50) | (66)
Asset backed securities |  |
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract] |  |
Estimated Fair Value - Less than 12 Months | 199 | 234
Estimated Fair Value - 12 Months or More | 442 | 1,112
Estimated Fair Value | 641 | 1,346
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Gross Unrealized Losses - Less than 12 Months | (3) | (1)
Gross Unrealized Losses - 12 Months or More | (24) | (54)
Gross Unrealized Losses | (27) | (55)
Commercial mortgage backed securities |  |
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract] |  |
Estimated Fair Value - Less than 12 Months | 176 | 100
Estimated Fair Value - 12 Months or More | 644 | 909
Estimated Fair Value | 820 | 1,009
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Gross Unrealized Losses - Less than 12 Months | (1) | (1)
Gross Unrealized Losses - 12 Months or More | (16) | (33)
Gross Unrealized Losses | (17) | (34)
Municipal bonds |  |
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract] |  |
Estimated Fair Value - Less than 12 Months | 1 | 20
Estimated Fair Value - 12 Months or More | 185 | 215
Estimated Fair Value | 186 | 235
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Gross Unrealized Losses - Less than 12 Months | 0 | (1)
Gross Unrealized Losses - 12 Months or More | (11) | (19)
Gross Unrealized Losses | (11) | (20)
Short-term investments |  |
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract] |  |
Estimated Fair Value - Less than 12 Months | 362 | 302
Estimated Fair Value - 12 Months or More | 0 | 0
Estimated Fair Value | 362 | 302
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Gross Unrealized Losses - Less than 12 Months | (2) | (2)
Gross Unrealized Losses - 12 Months or More | 0 | 0
Gross Unrealized Losses | $ (2) | $ (2)

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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 55 -Paragraph 8 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479081/326-30-55-8 Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 7 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481800/320-10-50-7 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479106/326-30-50-5 + Details
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