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