Claim and Claim Adjustment Expense Reserves and Future Policy Benefit Reserves (Commercial - Commercial Auto - Short Duration Contracts) (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	$ 19,908	$ 19,205	$ 18,701	$ 17,885
Commercial
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	8,430	$ 8,065
Commercial Auto | Commercial
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	787
General Liability | Commercial
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	3,206
Workers' Compensation | Commercial
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	3,739
Property and Other | Commercial
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	$ 698