Business Segments (Balance Sheet Information) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022		Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Reinsurance receivables	$ 5,434	$ 5,438		$ 5,484
Insurance receivables	3,470	3,187		2,974
Deferred acquisition costs	896	806	[1]	737
Goodwill	146	144	[1]	148
Deferred non-insurance warranty acquisition expense	3,661	3,671	[1]	3,476
Insurance reserves
Claim and claim adjustment expenses	23,304	22,120	[1]	21,268
Unearned premiums	6,933	6,374	[1]	5,761
Future policy benefits				18,298
Future policy benefits	13,959	13,480	[1]	18,010	$ 19,132
Deferred non-insurance warranty revenue	4,694	4,714	[1]	4,503
Operating Segments | Specialty
Segment Reporting Information [Line Items]
Reinsurance receivables	1,281	1,384		1,200
Insurance receivables	1,053	1,082		1,136
Deferred acquisition costs	392	381		363
Goodwill	117	117		117
Deferred non-insurance warranty acquisition expense	3,661	3,671		3,476
Insurance reserves
Claim and claim adjustment expenses	7,131	6,878		6,433
Unearned premiums	3,227	3,193		3,001
Future policy benefits				0
Future policy benefits	0	0
Deferred non-insurance warranty revenue	4,694	4,714		4,503
Operating Segments | Commercial
Segment Reporting Information [Line Items]
Reinsurance receivables	1,218	1,062		923
Insurance receivables	2,024	1,728		1,488
Deferred acquisition costs	371	321		278
Goodwill	0	0		0
Deferred non-insurance warranty acquisition expense	0	0		0
Insurance reserves
Claim and claim adjustment expenses	10,103	9,395		8,890
Unearned premiums	2,858	2,425		2,066
Future policy benefits				0
Future policy benefits	0	0
Deferred non-insurance warranty revenue	0	0		0
Operating Segments | International
Segment Reporting Information [Line Items]
Reinsurance receivables	468	414		381
Insurance receivables	388	369		340
Deferred acquisition costs	133	104		96
Goodwill	29	27		31
Deferred non-insurance warranty acquisition expense	0	0		0
Insurance reserves
Claim and claim adjustment expenses	2,709	2,403		2,280
Unearned premiums	749	653		585
Future policy benefits				0
Future policy benefits	0	0
Deferred non-insurance warranty revenue	0	0		0
Operating Segments | Life & Group
Segment Reporting Information [Line Items]
Reinsurance receivables	93	101		401
Insurance receivables	5	8		6
Deferred acquisition costs	0	0		0
Goodwill	0	0		0
Deferred non-insurance warranty acquisition expense	0	0		0
Insurance reserves
Claim and claim adjustment expenses	675	695		848
Unearned premiums	99	103		109
Future policy benefits				18,298
Future policy benefits	13,959	13,480
Deferred non-insurance warranty revenue	0	0		0
Operating Segments | Corporate & Other
Segment Reporting Information [Line Items]
Reinsurance receivables	2,374	2,477		2,579
Insurance receivables	0	0		4
Deferred acquisition costs	0	0		0
Goodwill	0	0		0
Deferred non-insurance warranty acquisition expense	0	0		0
Insurance reserves
Claim and claim adjustment expenses	2,686	2,749		2,817
Unearned premiums	0	0		0
Future policy benefits				0
Future policy benefits	0	0
Deferred non-insurance warranty revenue	0	0		0
Eliminations
Segment Reporting Information [Line Items]
Reinsurance receivables	0	0		0
Insurance receivables	0	0		0
Deferred acquisition costs	0	0		0
Goodwill	0	0		0
Deferred non-insurance warranty acquisition expense	0	0		0
Insurance reserves
Claim and claim adjustment expenses	0	0		0
Unearned premiums	0	0		0
Future policy benefits				0
Future policy benefits	0	0
Deferred non-insurance warranty revenue	$ 0	$ 0		$ 0

[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.