Income Taxes (Details) - Effective Tax Rate - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2023	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
U.S. income before income taxes		$ 5,947	$ 3,122	$ 3,101
Foreign income before income taxes		233	249	253
Income before income taxes		$ 6,180	$ 3,371	$ 3,354
Statutory tax rate (percent)		21.00%	21.00%	21.00%
Expected federal income tax expense		$ 1,298	$ 708	$ 704
Tax effect of nontaxable investment income		(122)	(132)	(149)
Tax effect of audit reserve		9	(205)	(40)
Tax effect of other, net		(4)	9	(3)
Total income tax expense included in the consolidated statement of income		$ 1,181	$ 380	$ 512
Effective tax rate (percent)		19.00%	11.00%	15.00%
Tax benefit due to the expiration of the statute of limitations with respect to a tax item impacted by the repeal of Internal Revenue Code Section 847, which related to the discounting of property-casualty loss reserves	$ 211
Income taxes paid		$ 1,310	$ 201	$ 817
Current income tax payable		$ 301	$ 285