Business Segments (Balance Sheet Information) (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023	Jun. 30, 2023
Segment Reporting Information [Line Items]
Reinsurance receivables	$ 5,674	$ 5,434
Insurance receivables	3,841	3,470
Deferred acquisition costs	948	896
Goodwill	146	146
Deferred non-insurance warranty acquisition expense	3,598	3,661
Insurance reserves
Claim and claim adjustment expenses	23,974	23,304
Unearned premiums	7,409	6,933
Future policy benefits	13,211	13,959	$ 13,666
Deferred non-insurance warranty revenue	4,623	4,694
Operating Segments | Specialty
Segment Reporting Information [Line Items]
Reinsurance receivables	1,513	1,281
Insurance receivables	1,020	1,053
Deferred acquisition costs	405	392
Goodwill	117	117
Deferred non-insurance warranty acquisition expense	3,598	3,661
Insurance reserves
Claim and claim adjustment expenses	7,319	7,131
Unearned premiums	3,197	3,227
Future policy benefits	0	0
Deferred non-insurance warranty revenue	4,623	4,694
Operating Segments | Commercial
Segment Reporting Information [Line Items]
Reinsurance receivables	1,306	1,218
Insurance receivables	2,375	2,024
Deferred acquisition costs	407	371
Goodwill	0	0
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	10,617	10,103
Unearned premiums	3,318	2,858
Future policy benefits	0	0
Deferred non-insurance warranty revenue	0	0
Operating Segments | International
Segment Reporting Information [Line Items]
Reinsurance receivables	487	468
Insurance receivables	441	388
Deferred acquisition costs	136	133
Goodwill	29	29
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	2,783	2,709
Unearned premiums	787	749
Future policy benefits	0	0
Deferred non-insurance warranty revenue	0	0
Operating Segments | Life & Group
Segment Reporting Information [Line Items]
Reinsurance receivables	90	93
Insurance receivables	4	5
Deferred acquisition costs	0	0
Goodwill	0	0
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	651	675
Unearned premiums	107	99
Future policy benefits	13,211	13,959
Deferred non-insurance warranty revenue	0	0
Operating Segments | Corporate & Other
Segment Reporting Information [Line Items]
Reinsurance receivables	2,278	2,374
Insurance receivables	1	0
Deferred acquisition costs	0	0
Goodwill	0	0
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	2,604	2,686
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