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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 | 12 Months Ended
--- | ---
Dec. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023
Assets |  |  |
Balance at beginning of period | $ 802 | $ 676 | $ 618
Total gains (losses) included in: Net income | 36 | 23 | 40
Total gains (losses) included in: OCI | 6 | (1) | 2
Transfers Into Level 3 | 39 | 0 | 16
Transfers Out of Level 3 | (379) | 0 | 0
Transfers (to) from held for sale |  | 0 |
Purchases | 153 | 191 | 122
Sales | (117) | (76) | (101)
Settlements | (56) | (11) | (21)
Balance at end of period | $ 484 | $ 802 | $ 676
Liabilities |  |  |
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] | Allstate Protection and Run-off Property-Liability net investment income, Net gains (losses) on investments and derivatives | Allstate Protection and Run-off Property-Liability net investment income, Net gains (losses) on investments and derivatives | Allstate Protection and Run-off Property-Liability net investment income, Net gains (losses) on investments and derivatives
Balance at the beginning of the period | $ 0 | $ 0 | $ 0
Total gains (losses) included in: net income | (1) | 0 | 0
Total gains (losses) included in: OCI | 0 | 0 | 0
Transfers into Level 3 | 0 | 0 | 0
Transfers out of Level 3 | 0 | 0 | 0
Transfers (to) from held for sale |  | 0 |
Purchases | 0 | 0 | 0
Sales | 0 | 0 | 0
Settlements | 0 | 0 | 0
Balance at the end of the period | $ (1) | $ 0 | $ 0
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] | Allstate Protection and Run-off Property-Liability net investment income | Allstate Protection and Run-off Property-Liability net investment income | Allstate Protection and Run-off Property-Liability net investment income
Gain (loss) included in earnings | $ 1 | $ (8) | $ (1)
Net gains (losses) on investments and derivatives |  |  |
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 gains (losses) on investments and derivatives | Net gains (losses) on investments and derivatives | Net gains (losses) on investments and derivatives
Gain (loss) included in earnings | $ 21 | $ 15 | $ 26
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
Gain (loss) included in earnings | $ 13 | $ 16 | $ 15
Other liabilities |  |  |
Assets |  |  |
Total gains (losses) included in: Net income | (1) |  |
Liabilities |  |  |
Balance at the beginning of the period | 0 |  |
Total gains (losses) included in: OCI | 0 |  |
Transfers into Level 3 | 0 |  |
Transfers out of Level 3 | 0 |  |
Purchases | 0 |  |
Sales | 0 |  |
Settlements | 0 |  |
Balance at the end of the period | (1) | 0 |
Municipal |  |  |
Assets |  |  |
Balance at beginning of period | 2 | 11 | 21
Total gains (losses) included in: Net income | 0 | (2) | 3
Total gains (losses) included in: OCI | 0 | 1 | (1)
Transfers Into Level 3 | 1 | 0 | 0
Transfers Out of Level 3 | 0 | 0 | 0
Transfers (to) from held for sale |  | 0 |
Purchases | 26 | 0 | 0
Sales | 0 | (5) | (10)
Settlements | 0 | (3) | (2)
Balance at end of period | 29 | 2 | 11
Corporate - public |  |  |
Assets |  |  |
Balance at beginning of period | 22 | 26 | 69
Total gains (losses) included in: Net income | (1) | 1 | (1)
Total gains (losses) included in: OCI | 1 | 0 | 2
Transfers Into Level 3 | 0 | 0 | 0
Transfers Out of Level 3 | (7) | 0 | 0
Transfers (to) from held for sale |  | (7) |
Purchases | 11 | 16 | 0
Sales | (11) | (14) | (44)
Settlements | (3) | 0 | 0
Balance at end of period | 12 | 22 | 26
Corporate - privately placed |  |  |
Assets |  |  |
Balance at beginning of period | 110 | 58 | 55
Total gains (losses) included in: Net income | (4) | (6) | (12)
Total gains (losses) included in: OCI | 4 | (2) | 1
Transfers Into Level 3 | 12 | 0 | 16
Transfers Out of Level 3 | 0 | 0 | 0
Transfers (to) from held for sale |  | 0 |
Purchases | 83 | 64 | 1
Sales | 0 | (2) | (3)
Settlements | (18) | (2) | 0
Balance at end of period | 187 | 110 | 58
ABS |  |  |
Assets |  |  |
Balance at beginning of period | 26 |  |
Total gains (losses) included in: Net income | 0 |  |
Total gains (losses) included in: OCI | 0 |  |
Transfers Into Level 3 | 26 |  |
Transfers Out of Level 3 | (41) |  |
Purchases | 15 |  |
Sales | 0 |  |
Settlements | (4) |  |
Balance at end of period | 22 | 26 |
MBS |  |  |
Assets |  |  |
Balance at beginning of period | 88 |  |
Total gains (losses) included in: Net income | 0 |  |
Total gains (losses) included in: OCI | 0 |  |
Transfers Into Level 3 | 0 |  |
Transfers Out of Level 3 | 0 |  |
Purchases | 0 |  |
Sales | 0 |  |
Settlements | (30) |  |
Balance at end of period | 58 | 88 |
ABS and MBS |  |  |
Assets |  |  |
Balance at beginning of period | 114 | 58 | 28
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 |  | 0 |
Purchases |  | 59 | 31
Sales |  | 0 | 0
Settlements |  | (3) | (1)
Balance at end of period |  | 114 | 58
Fixed income securities |  |  |
Assets |  |  |
Balance at beginning of period | 248 | 153 | 173
Total gains (losses) included in: Net income | (5) | (7) | (10)
Total gains (losses) included in: OCI | 5 | (1) | 2
Transfers Into Level 3 | 39 | 0 | 16
Transfers Out of Level 3 | (48) | 0 | 0
Transfers (to) from held for sale |  | (7) |
Purchases | 135 | 139 | 32
Sales | (11) | (21) | (57)
Settlements | (55) | (8) | (3)
Balance at end of period | 308 | 248 | 153
Equity securities |  |  |
Assets |  |  |
Balance at beginning of period | 407 | 402 | 333
Total gains (losses) included in: Net income | 28 | 8 | 36
Total gains (losses) included in: OCI | 0 | 0 | 0
Transfers Into Level 3 | 0 | 0 | 0
Transfers Out of Level 3 | (331) | 0 | 0
Transfers (to) from held for sale |  | 0 |
Purchases | 7 | 25 | 77
Sales | (89) | (28) | (44)
Settlements | 0 | 0 | 0
Balance at end of period | 22 | 407 | 402
Short-term investments |  |  |
Assets |  |  |
Balance at beginning of period | 5 | 1 | 6
Total gains (losses) included in: Net income | 0 | 0 | 0
Total gains (losses) included in: OCI | 0 | 0 | 0
Transfers Into Level 3 | 0 | 0 | 0
Transfers Out of Level 3 | 0 | 0 | 0
Transfers (to) from held for sale |  | 0 |
Purchases | 11 | 27 | 13
Sales | (9) | (20) | 0
Settlements | (1) | (3) | (18)
Balance at end of period | 6 | 5 | 1
Other investments |  |  |
Assets |  |  |
Balance at beginning of period | 1 | 2 | 3
Total gains (losses) included in: Net income | 0 | 6 | (1)
Total gains (losses) included in: OCI | 0 | 0 | 0
Transfers Into Level 3 | 0 | 0 | 0
Transfers Out of Level 3 | 0 | 0 | 0
Transfers (to) from held for sale |  | 0 |
Purchases | 0 | 0 | 0
Sales | 0 | (7) | 0
Settlements | 0 | 0 | 0
Balance at end of period | 1 | 1 | 2
Other assets |  |  |
Assets |  |  |
Balance at beginning of period | 134 | 118 | 103
Total gains (losses) included in: Net income | 13 | 16 | 15
Total gains (losses) included in: OCI | 0 | 0 | 0
Transfers Into Level 3 | 0 |  | 0
Transfers Out of Level 3 | 0 |  | 0
Transfers (to) from held for sale |  | 0 |
Purchases | 0 |  | 0
Sales | 0 |  | 0
Settlements | 0 |  | 0
Balance at end of period | 147 | 134 | 118
Assets held for sale |  |  |
Assets |  |  |
Balance at beginning of period | 7 | 0 |
Total gains (losses) included in: Net income | 0 | 0 |
Total gains (losses) included in: OCI | 1 | 0 |
Transfers Into Level 3 | 0 | 0 |
Transfers Out of Level 3 | 0 | 0 |
Transfers (to) from held for sale |  | 7 |
Purchases | 0 | 0 |
Sales | (8) | 0 |
Settlements | 0 | 0 |
Balance at end of period | $ 0 | $ 7 | $ 0

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