Business Segments (Balance Sheet Information) (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024	Sep. 30, 2024
Segment Reporting Information [Line Items]
Reinsurance receivables	$ 6,467	$ 6,072
Insurance receivables	3,693	3,697
Deferred acquisition costs	985	959
Goodwill	148	145
Deferred non-insurance warranty acquisition expense	3,340	3,525
Insurance reserves
Claim and claim adjustment expenses	26,525	24,976
Unearned premiums	7,578	7,346
Future policy benefits	13,546	13,158	$ 14,047
Deferred non-insurance warranty revenue	4,294	4,530
Operating Segments | Specialty
Segment Reporting Information [Line Items]
Reinsurance receivables	1,803	1,405
Insurance receivables	1,008	1,062
Deferred acquisition costs	447	427
Goodwill	117	117
Deferred non-insurance warranty acquisition expense	3,340	3,525
Insurance reserves
Claim and claim adjustment expenses	7,769	7,426
Unearned premiums	3,295	3,275
Future policy benefits	0	0
Deferred non-insurance warranty revenue	4,294	4,530
Operating Segments | Commercial
Segment Reporting Information [Line Items]
Reinsurance receivables	1,786	1,710
Insurance receivables	2,277	2,219
Deferred acquisition costs	395	405
Goodwill	0	0
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	12,153	11,336
Unearned premiums	3,392	3,252
Future policy benefits	0	0
Deferred non-insurance warranty revenue	0	0
Operating Segments | International
Segment Reporting Information [Line Items]
Reinsurance receivables	559	539
Insurance receivables	406	410
Deferred acquisition costs	143	127
Goodwill	31	28
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	3,315	2,920
Unearned premiums	796	727
Future policy benefits	0	0
Deferred non-insurance warranty revenue	0	0
Operating Segments | Life & Group
Segment Reporting Information [Line Items]
Reinsurance receivables	77	82
Insurance receivables	1	4
Deferred acquisition costs	0	0
Goodwill	0	0
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	615	622
Unearned premiums	95	92
Future policy benefits	13,546	13,158
Deferred non-insurance warranty revenue	0	0
Operating Segments | Corporate & Other
Segment Reporting Information [Line Items]
Reinsurance receivables	2,242	2,336
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	2,673	2,672
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