Business Segments (Balance Sheet Information) (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023
Segment Reporting Information [Line Items]
Reinsurance receivables	$ 5,820	$ 5,434
Insurance receivables	3,514	3,470
Deferred acquisition costs	943	896
Goodwill	147	146
Deferred non-insurance warranty acquisition expense	3,571	3,661
Insurance reserves
Claim and claim adjustment expenses	24,558	23,304
Unearned premiums	7,259	6,933
Future policy benefits	14,047	13,959	$ 12,654
Deferred non-insurance warranty revenue	4,594	4,694
Operating Segments | Specialty
Segment Reporting Information [Line Items]
Reinsurance receivables	1,509	1,281
Insurance receivables	986	1,053
Deferred acquisition costs	413	392
Goodwill	117	117
Deferred non-insurance warranty acquisition expense	3,571	3,661
Insurance reserves
Claim and claim adjustment expenses	7,328	7,131
Unearned premiums	3,218	3,227
Future policy benefits	0	0
Deferred non-insurance warranty revenue	4,594	4,694
Operating Segments | Commercial
Segment Reporting Information [Line Items]
Reinsurance receivables	1,456	1,218
Insurance receivables	2,149	2,024
Deferred acquisition costs	400	371
Goodwill	0	0
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	11,018	10,103
Unearned premiums	3,186	2,858
Future policy benefits	0	0
Deferred non-insurance warranty revenue	0	0
Operating Segments | International
Segment Reporting Information [Line Items]
Reinsurance receivables	533	468
Insurance receivables	375	388
Deferred acquisition costs	130	133
Goodwill	30	29
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	2,990	2,709
Unearned premiums	755	749
Future policy benefits	0	0
Deferred non-insurance warranty revenue	0	0
Operating Segments | Life & Group
Segment Reporting Information [Line Items]
Reinsurance receivables	86	93
Insurance receivables	3	5
Deferred acquisition costs	0	0
Goodwill	0	0
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	650	675
Unearned premiums	100	99
Future policy benefits	14,047	13,959
Deferred non-insurance warranty revenue	0	0
Operating Segments | Corporate & Other
Segment Reporting Information [Line Items]
Reinsurance receivables	2,236	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	2,572	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