Business Segments (Balance Sheet Information) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023
Segment Reporting Information [Line Items]
Reinsurance receivables	$ 5,596	$ 5,434
Insurance receivables	3,458	3,470
Deferred acquisition costs	927	896
Goodwill	146	146
Deferred non-insurance warranty acquisition expense	3,621	3,661
Insurance reserves
Claim and claim adjustment expenses	23,588	23,304
Unearned premiums	7,046	6,933
Future policy benefits	13,513	13,959	$ 13,976
Deferred non-insurance warranty revenue	4,645	4,694
Operating Segments | Specialty
Segment Reporting Information [Line Items]
Reinsurance receivables	1,432	1,281
Insurance receivables	979	1,053
Deferred acquisition costs	401	392
Goodwill	117	117
Deferred non-insurance warranty acquisition expense	3,621	3,661
Insurance reserves
Claim and claim adjustment expenses	7,221	7,131
Unearned premiums	3,193	3,227
Future policy benefits	0	0
Deferred non-insurance warranty revenue	4,645	4,694
Operating Segments | Commercial
Segment Reporting Information [Line Items]
Reinsurance receivables	1,279	1,218
Insurance receivables	2,096	2,024
Deferred acquisition costs	394	371
Goodwill	0	0
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	10,332	10,103
Unearned premiums	2,996	2,858
Future policy benefits	0	0
Deferred non-insurance warranty revenue	0	0
Operating Segments | International
Segment Reporting Information [Line Items]
Reinsurance receivables	477	468
Insurance receivables	379	388
Deferred acquisition costs	132	133
Goodwill	29	29
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	2,745	2,709
Unearned premiums	740	749
Future policy benefits	0	0
Deferred non-insurance warranty revenue	0	0
Operating Segments | Life & Group
Segment Reporting Information [Line Items]
Reinsurance receivables	92	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	663	675
Unearned premiums	118	99
Future policy benefits	13,513	13,959
Deferred non-insurance warranty revenue	0	0
Operating Segments | Corporate & Other
Segment Reporting Information [Line Items]
Reinsurance receivables	2,316	2,374
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	2,627	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	(1)	0
Future policy benefits	0	0
Deferred non-insurance warranty revenue	$ 0	$ 0