Business Segments (Balance Sheet Information) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022		Sep. 30, 2022	Dec. 31, 2020
Segment Reporting Information [Line Items]
Reinsurance receivables	$ 5,469	$ 5,438
Insurance receivables	3,240	3,187
Deferred acquisition costs	880	806	[1]
Goodwill	145	144	[1]
Deferred non-insurance warranty acquisition expense	3,688	3,671	[1]
Insurance reserves
Claim and claim adjustment expenses	22,836	22,120	[1]
Unearned premiums	6,789	6,374	[1]
Future policy benefits	12,654	13,480	[1]	$ 13,181	$ 19,132
Deferred non-insurance warranty revenue	4,736	4,714	[1]
Operating Segments | Specialty
Segment Reporting Information [Line Items]
Reinsurance receivables	1,384	1,384
Insurance receivables	1,010	1,082
Deferred acquisition costs	398	381
Goodwill	117	117
Deferred non-insurance warranty acquisition expense	3,688	3,671
Insurance reserves
Claim and claim adjustment expenses	7,090	6,878
Unearned premiums	3,202	3,193
Future policy benefits	0	0
Deferred non-insurance warranty revenue	4,736	4,714
Operating Segments | Commercial
Segment Reporting Information [Line Items]
Reinsurance receivables	1,217	1,062
Insurance receivables	1,880	1,728
Deferred acquisition costs	358	321
Goodwill	0	0
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	9,902	9,395
Unearned premiums	2,764	2,425
Future policy benefits	0	0
Deferred non-insurance warranty revenue	0	0
Operating Segments | International
Segment Reporting Information [Line Items]
Reinsurance receivables	455	414
Insurance receivables	346	369
Deferred acquisition costs	124	104
Goodwill	28	27
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	2,572	2,403
Unearned premiums	717	653
Future policy benefits	0	0
Deferred non-insurance warranty revenue	0	0
Operating Segments | Life & Group
Segment Reporting Information [Line Items]
Reinsurance receivables	97	101
Insurance receivables	4	8
Deferred acquisition costs	0	0
Goodwill	0	0
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	649	695
Unearned premiums	106	103
Future policy benefits	12,654	13,480
Deferred non-insurance warranty revenue	0	0
Operating Segments | Corporate & Other
Segment Reporting Information [Line Items]
Reinsurance receivables	2,316	2,477
Insurance receivables	0	0
Deferred acquisition costs	0	0
Goodwill	0	0
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	2,623	2,749
Unearned premiums	0	0
Future policy benefits	0	0
Deferred non-insurance warranty revenue	0	0
Eliminations
Segment Reporting Information [Line Items]
Reinsurance receivables	0	0
Insurance receivables	0	0
Deferred acquisition costs	0	0
Goodwill	0	0
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	0	0
Unearned premiums	0	0
Future policy benefits	0	0
Deferred non-insurance warranty revenue	$ 0	$ 0

[1] As of January 1, 2023, the Company adopted 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 Condensed Consolidated Financial Statements for additional information.