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Employee Benefit Plans - Narrative (Details) |  | 12 Months Ended
--- | --- | ---
Feb. 14, 2024 $ / shares | Dec. 31, 2023 USD ($) plan $ / shares | Dec. 31, 2022 USD ($) $ / shares | Dec. 31, 2021 USD ($) $ / shares
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Employer contributions |  | $ 0 | $ 0 | $ 0
Expected contributions expected in the next fiscal year |  | $ 0 |  |
Percentage within which the planned allocation is managed |  | 5.00% |  |
Investments at Fair Value |  | $ 2,422,000,000 | $ 2,327,000,000 |
Common stock dividends, per share (in dollars per share) | $ / shares |  | $ 0.44 | $ 0.40 | $ 0.37
Subsequent Event |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Increase in quarterly cash dividend percentage | 9.00% |  |  |
Common stock dividends, per share (in dollars per share) | $ / shares | $ 0.12 |  |  |
Growth-Oriented |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Target allocation percentage of pension plan assets |  | 55.00% |  |
Investments at Fair Value |  | $ 1,271,000,000 | $ 1,434,000,000 |
Immunizing |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Target allocation percentage of pension plan assets |  | 45.00% |  |
Investments at Fair Value |  | $ 1,151,000,000 | 893,000,000 |
Pension Plan |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Employer contributions |  | 20,000,000 | 18,000,000 |
Net actuarial gain (loss) |  | $ (20,000,000) | $ 570,000,000 |
Increase (decrease) in weighted average discount rate |  | 0.20% | (2.24%) |
Investments at Fair Value |  | $ 2,422,000,000 | $ 2,327,000,000 | $ 3,016,000,000
Pre-tax (loss) gain to be amortized related to post-retirement obligations |  | (623,000,000) |  |
Plan benefit accruals |  | 2,343,000,000 | 2,368,000,000 | 3,022,000,000
Defined benefit plan, service cost |  | 24,000,000 | 32,000,000 | 41,000,000
Accumulated Benefit Obligation |  | $ 2,252,000,000 | 2,285,000,000 |
Pension Plan | Quality Carriers, Inc. | Multiemployer Plan, Union-represented Employees |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Number of multi-employer pension plans | plan |  | 2 |  |
Contingent liability for full withdrawal or termination of multi-employer plan |  | $ 334,000,000 |  |
Pension Plan | Quality Carriers, Inc. | Multiemployer Plan, Union-represented Employees, Central Southeast and Southwest Areas Pension Plan |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Contingent liability for full withdrawal or termination of multi-employer plan |  | 328,000,000 |  |
Postretirement Health Coverage |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined benefit plan, expected future benefit payments |  | 50,000,000 |  |
Accumulated Benefit Obligation |  | 56,000,000 | 61,000,000 |
Other Postretirement Benefits Plan |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Premium expense incurred under the plan |  | 11,000,000 | 13,000,000 | 21,000,000
Savings Plan |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Expense associated with savings plans |  | $ 35,000,000 | $ 28,000,000 | $ 29,000,000

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