Summary of Significant Accounting Policies (Effects of Adoption of ASU 2018-12, Balance Sheet) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022		Dec. 31, 2021		Dec. 31, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred income taxes	$ 1,016	$ 1,251	[1]
Total assets	64,711	61,000	[1]
Claim and claim adjustment expenses	23,304	22,120	[1]	$ 21,268
Future policy benefits	13,959	13,480	[1]	18,010		$ 19,132
Total liabilities	54,818	52,452	[1]
Retained earnings	9,755	9,336	[1]
Accumulated other comprehensive loss	(2,672)	(3,598)	[1]
Total stockholders' equity	$ 9,893	8,548	[1]	$ 11,105	[1]
Prior to Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred income taxes		1,178
Total assets		60,927
Claim and claim adjustment expenses		25,099
Future policy benefits		10,151				$ 13,318
Total liabilities		52,102
Retained earnings		9,572
Accumulated other comprehensive loss		(3,557)
Total stockholders' equity		8,825
Effect of Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred income taxes		73
Total assets		73
Claim and claim adjustment expenses		(2,979)
Future policy benefits		3,329
Total liabilities		350
Retained earnings		(236)
Accumulated other comprehensive loss		(41)
Total stockholders' equity		$ (277)

[1] As of January 1, 2023, the Company adopted ASU 2018-12, Financial Services-Insurance (Topic 944): Targeted Improvements to the Accounting for Long-Duration Contracts (ASU 2018-12) using the modified retrospective method applied as of the transition date of January 1, 2021. Prior period amounts in the financial statements have been adjusted to reflect application of the new guidance. See Note A to the Consolidated Financial Statements for additional information.