Employee Benefit Plans - Narrative (Details)	12 Months Ended
	Dec. 31, 2022 USD ($) plan	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
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	$ 2,327,000,000	3,016,000,000
Growth-Oriented
Defined Benefit Plan Disclosure [Line Items]
Target allocation percentage of pension plan assets	60.00%
Investments at Fair Value	$ 1,434,000,000	1,812,000,000
Immunizing
Defined Benefit Plan Disclosure [Line Items]
Target allocation percentage of pension plan assets	40.00%
Investments at Fair Value	$ 893,000,000	1,204,000,000
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Net actuarial gain (loss)	$ 570,000,000	$ 142,000,000
Increase (decrease) in weighted average discount rate	2.24%	0.35%
Investments at Fair Value	$ 2,327,000,000	$ 3,016,000,000	3,000,000,000
Pre-tax (loss) gain to be amortized related to post-retirement obligations	(727,000,000)
Expense associated with savings plans	28,000,000	29,000,000	39,000,000
Plan benefit accruals	2,368,000,000	3,022,000,000	3,257,000,000
Defined benefit plan, service cost	32,000,000	41,000,000	43,000,000
Accumulated Benefit Obligation	$ 2,285,000,000	2,909,000,000
Pension Plan | Quality Carriers, Inc. | Multiemployer Plan, Union-represented Employees
Defined Benefit Plan Disclosure [Line Items]
Number of multi-employer pension plans | plan	3
Contingent liability for full withdrawal or termination of multi-employer plan	$ 336,000,000
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	55,000,000
Accumulated Benefit Obligation	61,000,000	81,000,000
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Premium expense incurred under the plan	$ 13,000,000	$ 21,000,000	$ 20,000,000