Summary of Significant Accounting Policies - Securities Loaned and Recognition of Premium Revenues and Contract Charges, and Related Benefits and Interest Credited and Deferred Policy Acquisition Costs (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Securities loaned
Cash collateral received as percentage of fair value of domestic securities loaned	102.00%
Cash collateral received as a percent of fair value of foreign securities loaned	105.00%
Deferred Policy Acquisition and Sales Inducement Costs
Decrease in unearned premiums	$ (2,385)	$ (2,539)	$ (1,608)
Unearned premium, year one	1,850
Unearned premium, year two	1,430
Unearned premium, thereafter	1,870
Present value of future profits	8	10
Amortization expense of present value of future profits	2	11	$ 324
Property and casualty insurance premiums | Protection Services
Deferred Policy Acquisition and Sales Inducement Costs
Decrease in unearned premiums	$ 1,740	$ 1,460
Minimum | Personal Lines
Deferred Policy Acquisition and Sales Inducement Costs
Property and casualty insurance contract, terms	6 months
Minimum | Protection Plans and Other Contracts
Deferred Policy Acquisition and Sales Inducement Costs
Period for amortization of DAC for property-liability insurance	1 year
Maximum
Securities loaned
Securities lending transactions length	30 days
Maximum | Personal Lines
Deferred Policy Acquisition and Sales Inducement Costs
Property and casualty insurance contract, terms	12 months
Maximum | Protection Plans and Other Contracts
Deferred Policy Acquisition and Sales Inducement Costs
Period for amortization of DAC for property-liability insurance	5 years