Reinsurance (Consolidated Reinsurance) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Premiums written [Abstract]
Direct	$ 42,811	$ 37,749	$ 36,848
Assumed	3,969	3,512	3,276
Ceded	(8,912)	(7,441)	(7,849)
Net	37,868	33,820	32,275
Premiums earned [Abstract]
Direct	41,138	37,037	35,876
Assumed	3,650	3,323	3,107
Ceded	(8,433)	(7,243)	(7,693)
Net premiums earned	36,355	33,117	31,290
Reinsurance recoveries on losses and loss expenses incurred	$ 6,100	$ 5,000	$ 4,900