Business Segments (Balance Sheet Information) (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Reinsurance receivables	$ 6,072	$ 5,434	$ 5,438
Insurance receivables	3,697	3,470	3,187
Deferred acquisition costs	959	896	806
Goodwill	145	146	144
Deferred non-insurance warranty acquisition expense	3,525	3,661	3,671
Insurance reserves
Claim and claim adjustment expenses	24,976	23,304	22,120
Unearned premiums	7,346	6,933	6,374
Future policy benefits			13,480
Future policy benefits	13,158	13,959	13,480
Deferred non-insurance warranty revenue	4,530	4,694	4,714
Operating Segments | Specialty
Segment Reporting Information [Line Items]
Reinsurance receivables	1,405	1,281	1,384
Insurance receivables	1,062	1,053	1,082
Deferred acquisition costs	427	392	381
Goodwill	117	117	117
Deferred non-insurance warranty acquisition expense	3,525	3,661	3,671
Insurance reserves
Claim and claim adjustment expenses	7,426	7,131	6,878
Unearned premiums	3,275	3,227	3,193
Future policy benefits			0
Future policy benefits	0	0
Deferred non-insurance warranty revenue	4,530	4,694	4,714
Operating Segments | Commercial
Segment Reporting Information [Line Items]
Reinsurance receivables	1,710	1,218	1,062
Insurance receivables	2,219	2,024	1,728
Deferred acquisition costs	405	371	321
Goodwill	0	0	0
Deferred non-insurance warranty acquisition expense	0	0	0
Insurance reserves
Claim and claim adjustment expenses	11,336	10,103	9,395
Unearned premiums	3,252	2,858	2,425
Future policy benefits			0
Future policy benefits	0	0
Deferred non-insurance warranty revenue	0	0	0
Operating Segments | International
Segment Reporting Information [Line Items]
Reinsurance receivables	539	468	414
Insurance receivables	410	388	369
Deferred acquisition costs	127	133	104
Goodwill	28	29	27
Deferred non-insurance warranty acquisition expense	0	0	0
Insurance reserves
Claim and claim adjustment expenses	2,920	2,709	2,403
Unearned premiums	727	749	653
Future policy benefits			0
Future policy benefits	0	0
Deferred non-insurance warranty revenue	0	0	0
Operating Segments | Life & Group
Segment Reporting Information [Line Items]
Reinsurance receivables	82	93	101
Insurance receivables	4	5	8
Deferred acquisition costs	0	0	0
Goodwill	0	0	0
Deferred non-insurance warranty acquisition expense	0	0	0
Insurance reserves
Claim and claim adjustment expenses	622	675	695
Unearned premiums	92	99	103
Future policy benefits			13,480
Future policy benefits	13,158	13,959
Deferred non-insurance warranty revenue	0	0	0
Operating Segments | Corporate & Other
Segment Reporting Information [Line Items]
Reinsurance receivables	2,336	2,374	2,477
Insurance receivables	2	0	0
Deferred acquisition costs	0	0	0
Goodwill	0	0	0
Deferred non-insurance warranty acquisition expense	0	0	0
Insurance reserves
Claim and claim adjustment expenses	2,672	2,686	2,749
Unearned premiums	0	0	0
Future policy benefits			0
Future policy benefits	0	0
Deferred non-insurance warranty revenue	0	0	0
Eliminations
Segment Reporting Information [Line Items]
Reinsurance receivables	0	0	0
Insurance receivables	0	0	0
Deferred acquisition costs	0	0	0
Goodwill	0	0	0
Deferred non-insurance warranty acquisition expense	0	0	0
Insurance reserves
Claim and claim adjustment expenses	0	0	0
Unearned premiums	0	0	0
Future policy benefits			0
Future policy benefits	0	0
Deferred non-insurance warranty revenue	$ 0	$ 0	$ 0