Business Segments (Balance sheet information) (Details) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
Reinsurance receivables	$ 5,774	$ 5,484
Insurance receivables	3,238	2,974
Deferred acquisition costs	792	737
Goodwill	145	148
Deferred non-insurance warranty acquisition expense	3,593	3,476
Insurance reserves
Claim and claim adjustment expenses	24,559	24,174
Unearned premiums	6,289	5,761
Future policy benefits	10,926	13,236
Deferred non-insurance warranty revenue	4,638	4,503
Operating Segments | Specialty
Segment Reporting Information [Line Items]
Reinsurance receivables	1,502	1,200
Insurance receivables	1,097	1,136
Deferred acquisition costs	375	363
Goodwill	117	117
Deferred non-insurance warranty acquisition expense	3,593	3,476
Insurance reserves
Claim and claim adjustment expenses	6,861	6,433
Unearned premiums	3,093	3,001
Future policy benefits	0	0
Deferred non-insurance warranty revenue	4,638	4,503
Operating Segments | Commercial
Segment Reporting Information [Line Items]
Reinsurance receivables	964	923
Insurance receivables	1,751	1,488
Deferred acquisition costs	314	278
Goodwill	0	0
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	8,954	8,890
Unearned premiums	2,428	2,066
Future policy benefits	0	0
Deferred non-insurance warranty revenue	0	0
Operating Segments | International
Segment Reporting Information [Line Items]
Reinsurance receivables	365	381
Insurance receivables	389	340
Deferred acquisition costs	103	96
Goodwill	28	31
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	2,307	2,280
Unearned premiums	650	585
Future policy benefits	0	0
Deferred non-insurance warranty revenue	0	0
Operating Segments | Life & Group
Segment Reporting Information [Line Items]
Reinsurance receivables	458	401
Insurance receivables	3	6
Deferred acquisition costs	0	0
Goodwill	0	0
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	3,670	3,754
Unearned premiums	118	109
Future policy benefits	10,926	13,236
Deferred non-insurance warranty revenue	0	0
Operating Segments | Corporate & Other
Segment Reporting Information [Line Items]
Reinsurance receivables	2,485	2,579
Insurance receivables	(2)	4
Deferred acquisition costs	0	0
Goodwill	0	0
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	2,767	2,817
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