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Fair Value of Assets and Liabilities - Schedule of Rollforward of Level 3 Assets and Liabilities Held at Fair Value (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2024 | Sep. 30, 2023
Assets |  |  |  |
Balance at beginning of period | $ 675 | $ 625 | $ 676 | $ 618
Total gains (losses) included in: Net income | 12 | 24 | 16 | 22
Total gains (losses) included in: OCI | 0 | (2) | 1 | 0
Transfers Into Level 3 | 0 | 0 | 0 | 16
Transfers Out of Level 3 | 0 | 0 | 0 | 0
Transfers (to) from held for sale | 0 |  | 0 |
Purchases | 39 | 14 | 94 | 92
Sales | (2) | (14) | (59) | (98)
Issues | 0 | 0 | 0 | 0
Settlements | (1) | 0 | (5) | (3)
Balance at end of period | $ 723 | $ 647 | $ 723 | $ 647
Net investment income |  |  |  |
Total Level 3 gains (losses) included in net income |  |  |  |
Fair Value, Asset (Liability), Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] | Net investment income | Net investment income | Net investment income | Net investment income
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] | Net investment income | Net investment income | Net investment income | Net investment income
Gain (loss) included in earnings | $ 0 | $ (1) | $ 1 | $ (3)
Net gains (losses) on investments and derivatives |  |  |  |
Total Level 3 gains (losses) included in net income |  |  |  |
Gain (loss) included in earnings | $ 10 | $ 16 | $ 10 | $ 15
Operating costs and expenses |  |  |  |
Total Level 3 gains (losses) included in net income |  |  |  |
Fair Value, Asset (Liability), Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] | Operating costs and expenses | Operating costs and expenses | Operating costs and expenses | Operating costs and expenses
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] | Operating costs and expenses | Operating costs and expenses | Operating costs and expenses | Operating costs and expenses
Gain (loss) included in earnings | $ 2 | $ 9 | $ 5 | $ 10
Municipal |  |  |  |
Assets |  |  |  |
Balance at beginning of period | 7 | 12 | 11 | 21
Total gains (losses) included in: Net income | (2) | 0 | (2) | 3
Total gains (losses) included in: OCI | 0 | 0 | 0 | (1)
Transfers Into Level 3 | 0 | 0 | 0 | 0
Transfers Out of Level 3 | 0 | 0 | 0 | 0
Transfers (to) from held for sale | 0 |  | 0 |
Purchases | 0 | 0 | 0 | 0
Sales | 0 | (1) | (2) | (10)
Issues | 0 | 0 | 0 | 0
Settlements | 0 | 0 | (2) | (2)
Balance at end of period | 5 | 11 | 5 | 11
Corporate - public |  |  |  |
Assets |  |  |  |
Balance at beginning of period | 30 | 26 | 26 | 69
Total gains (losses) included in: Net income | 0 | 0 | 1 | (1)
Total gains (losses) included in: OCI | 0 | (1) | 1 | 1
Transfers Into Level 3 | 0 | 0 | 0 | 0
Transfers Out of Level 3 | 0 | 0 | 0 | 0
Transfers (to) from held for sale | (7) |  | 7 |
Purchases | 5 | 0 | 16 | 0
Sales | 0 | 0 | (9) | (44)
Issues | 0 | 0 | 0 | 0
Settlements | 0 | 0 | 0 | 0
Balance at end of period | 28 | 25 | 28 | 25
Corporate - privately placed |  |  |  |
Assets |  |  |  |
Balance at beginning of period | 50 | 60 | 58 | 55
Total gains (losses) included in: Net income | 0 | 0 | (6) | (11)
Total gains (losses) included in: OCI | 0 | (1) | 0 | 0
Transfers Into Level 3 | 0 | 0 | 0 | 16
Transfers Out of Level 3 | 0 | 0 | 0 | 0
Transfers (to) from held for sale | 0 |  | 0 |
Purchases | 1 | 0 | 1 | 1
Sales | 0 | 0 | (2) | (2)
Issues | 0 | 0 | 0 | 0
Settlements | 0 | 0 | 0 | 0
Balance at end of period | 51 | 59 | 51 | 59
ABS |  |  |  |
Assets |  |  |  |
Balance at beginning of period | 71 | 34 | 58 | 28
Total gains (losses) included in: Net income | 0 | 0 | 0 | 0
Total gains (losses) included in: OCI | 0 | 0 | 0 | 0
Transfers Into Level 3 | 0 | 0 | 0 | 0
Transfers Out of Level 3 | 0 | 0 | 0 | 0
Transfers (to) from held for sale | 0 |  | 0 |
Purchases | 27 | 4 | 41 | 11
Sales | 0 | 0 | 0 | 0
Issues | 0 | 0 | 0 | 0
Settlements | (1) | 0 | (2) | (1)
Balance at end of period | 97 | 38 | 97 | 38
Fixed income securities |  |  |  |
Assets |  |  |  |
Balance at beginning of period | 158 | 132 | 153 | 173
Total gains (losses) included in: Net income | (2) | 0 | (7) | (9)
Total gains (losses) included in: OCI | 0 | (2) | 1 | 0
Transfers Into Level 3 | 0 | 0 | 0 | 16
Transfers Out of Level 3 | 0 | 0 | 0 | 0
Transfers (to) from held for sale | (7) |  | 7 |
Purchases | 33 | 4 | 58 | 12
Sales | 0 | (1) | (13) | (56)
Issues | 0 | 0 | 0 | 0
Settlements | (1) | 0 | (4) | (3)
Balance at end of period | 181 | 133 | 181 | 133
Equity securities |  |  |  |
Assets |  |  |  |
Balance at beginning of period | 393 | 381 | 402 | 333
Total gains (losses) included in: Net income | 12 | 15 | 18 | 22
Total gains (losses) included in: OCI | 0 | 0 | 0 | 0
Transfers Into Level 3 | 0 | 0 | 0 | 0
Transfers Out of Level 3 | 0 | 0 | 0 | 0
Transfers (to) from held for sale | 0 |  | 0 |
Purchases | 5 | 0 | 14 | 70
Sales | (2) | (13) | (26) | (42)
Issues | 0 | 0 | 0 | 0
Settlements | 0 | 0 | 0 | 0
Balance at end of period | 408 | 383 | 408 | 383
Short-term investments |  |  |  |
Assets |  |  |  |
Balance at beginning of period | 1 | 6 | 1 | 6
Total gains (losses) included in: Net income | 0 | 0 | 0 | 0
Total gains (losses) included in: OCI | 0 | 0 | 0 | 0
Transfers Into Level 3 | 0 | 0 | 0 | 0
Transfers Out of Level 3 | 0 | 0 | 0 | 0
Transfers (to) from held for sale | 0 |  | 0 |
Purchases | 1 | 10 | 22 | 10
Sales | 0 | 0 | (20) | 0
Issues | 0 | 0 | 0 | 0
Settlements | 0 | 0 | (1) | 0
Balance at end of period | 2 | 16 | 2 | 16
Other investments |  |  |  |
Assets |  |  |  |
Balance at beginning of period | 2 | 2 | 2 | 3
Total gains (losses) included in: Net income | 0 | 0 | 0 | (1)
Total gains (losses) included in: OCI | 0 | 0 | 0 | 0
Transfers Into Level 3 | 0 | 0 | 0 | 0
Transfers Out of Level 3 | 0 | 0 | 0 | 0
Transfers (to) from held for sale | 0 |  | 0 |
Purchases | 0 | 0 | 0 | 0
Sales | 0 | 0 | 0 | 0
Issues | 0 | 0 | 0 | 0
Settlements | 0 | 0 | 0 | 0
Balance at end of period | 2 | 2 | 2 | 2
Other assets |  |  |  |
Assets |  |  |  |
Balance at beginning of period | 121 | 104 | 118 | 103
Total gains (losses) included in: Net income | 2 | 9 | 5 | 10
Total gains (losses) included in: OCI | 0 | 0 | 0 | 0
Transfers Into Level 3 | 0 | 0 | 0 | 0
Transfers Out of Level 3 | 0 | 0 | 0 | 0
Transfers (to) from held for sale | 0 |  | 0 |
Purchases | 0 | 0 | 0 | 0
Sales | 0 | 0 | 0 | 0
Issues | 0 | 0 | 0 | 0
Settlements | 0 | 0 | 0 | 0
Balance at end of period | 123 | $ 113 | 123 | $ 113
Assets held for sale |  |  |  |
Assets |  |  |  |
Balance at beginning of period | 0 |  | 0 |
Total gains (losses) included in: Net income | 0 |  | 0 |
Total gains (losses) included in: OCI | 0 |  | 0 |
Transfers Into Level 3 | 0 |  | 0 |
Transfers Out of Level 3 | 0 |  | 0 |
Transfers (to) from held for sale | 7 |  | (7) |
Purchases | 0 |  | 0 |
Sales | 0 |  | 0 |
Issues | 0 |  | 0 |
Settlements | 0 |  | 0 |
Balance at end of period | $ 7 |  | $ 7 |

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