Business Segments (Balance sheet information) (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
Reinsurance receivables	$ 5,527	$ 5,484
Insurance receivables	2,920	2,974
Deferred acquisition costs	766	737
Goodwill	147	148
Deferred non-insurance warranty acquisition expense	3,504	3,476
Insurance reserves
Claim and claim adjustment expenses	24,348	24,174
Unearned premiums	5,942	5,761
Future policy benefits	11,938	13,236
Deferred non-insurance warranty revenue	4,528	4,503
Operating Segments | Specialty
Segment Reporting Information [Line Items]
Reinsurance receivables	1,291	1,200
Insurance receivables	1,055	1,136
Deferred acquisition costs	370	363
Goodwill	117	117
Deferred non-insurance warranty acquisition expense	3,504	3,476
Insurance reserves
Claim and claim adjustment expenses	6,623	6,433
Unearned premiums	3,029	3,001
Future policy benefits	0	0
Deferred non-insurance warranty revenue	4,528	4,503
Operating Segments | Commercial
Segment Reporting Information [Line Items]
Reinsurance receivables	947	923
Insurance receivables	1,503	1,488
Deferred acquisition costs	294	278
Goodwill	0	0
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	8,934	8,890
Unearned premiums	2,161	2,066
Future policy benefits	0	0
Deferred non-insurance warranty revenue	0	0
Operating Segments | International
Segment Reporting Information [Line Items]
Reinsurance receivables	360	381
Insurance receivables	359	340
Deferred acquisition costs	102	96
Goodwill	30	31
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	2,316	2,280
Unearned premiums	624	585
Future policy benefits	0	0
Deferred non-insurance warranty revenue	0	0
Operating Segments | Life & Group
Segment Reporting Information [Line Items]
Reinsurance receivables	399	401
Insurance receivables	4	6
Deferred acquisition costs	0	0
Goodwill	0	0
Deferred non-insurance warranty acquisition expense	0	0
Insurance reserves
Claim and claim adjustment expenses	3,712	3,754
Unearned premiums	128	109
Future policy benefits	11,938	13,236
Deferred non-insurance warranty revenue	0	0
Operating Segments | Corporate & Other
Segment Reporting Information [Line Items]
Reinsurance receivables	2,530	2,579
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	2,763	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