Business Segments (Balance Sheet Information) (Details) - USD ($) $ in Millions	Jun. 30, 2026	Dec. 31, 2025	Jun. 30, 2025
Segment Reporting [Line Items]
Reinsurance receivables	$ 6,524	$ 6,408
Insurance receivables	4,224	3,764
Deferred acquisition costs	1,026	986
Goodwill	147	148
Deferred non-insurance warranty acquisition expense	2,981	3,220
Insurance reserves
Claim and claim adjustment expenses	27,490	26,599
Unearned premiums	8,035	7,635
Future policy benefits	13,262	13,448	$ 13,329
Deferred non-insurance warranty revenue	3,798	4,138
Operating Segments | Specialty
Segment Reporting [Line Items]
Reinsurance receivables	1,723	1,716
Insurance receivables	926	1,008
Deferred acquisition costs	462	447
Goodwill	117	117
Deferred non-insurance warranty acquisition expense	2,981	3,220
Insurance reserves
Claim and claim adjustment expenses	8,013	7,784
Unearned premiums	3,314	3,317
Future policy benefits	0	0
Deferred non-insurance warranty revenue	3,798	4,138
Operating Segments | Commercial
Segment Reporting [Line Items]
Reinsurance receivables	1,933	1,762
Insurance receivables	2,799	2,315
Deferred acquisition costs	412	391
Goodwill	0	0
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	12,892	12,249
Unearned premiums	3,764	3,411
Future policy benefits	0	0
Deferred non-insurance warranty revenue	0	0
Operating Segments | International
Segment Reporting [Line Items]
Reinsurance receivables	623	577
Insurance receivables	498	438
Deferred acquisition costs	152	148
Goodwill	30	31
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	3,496	3,376
Unearned premiums	860	819
Future policy benefits	0	0
Deferred non-insurance warranty revenue	0	0
Operating Segments | Life & Group
Segment Reporting [Line Items]
Reinsurance receivables	54	56
Insurance receivables	1	2
Deferred acquisition costs	0	0
Goodwill	0	0
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	575	591
Unearned premiums	97	88
Future policy benefits	13,262	13,448
Deferred non-insurance warranty revenue	0	0
Operating Segments | Corporate & Other
Segment Reporting [Line Items]
Reinsurance receivables	2,191	2,297
Insurance receivables	0	1
Deferred acquisition costs	0	0
Goodwill	0	0
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	2,514	2,599
Unearned premiums	0	0
Future policy benefits	0	0
Deferred non-insurance warranty revenue	0	0
Eliminations
Segment Reporting [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