Reinsurance (Summary Of Direct, Assumed And Ceded Premiums Written And Earned) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reinsurance Disclosures [Abstract]
Direct - Premium written	$ 93,953	$ 84,835	$ 83,974
Assumed - Premium written	822	264	275
Ceded - Premium written	(45)	(51)	(44)
Net premiums - written	$ 94,730	$ 85,048	$ 84,205
Percentage - assumed to net premiums - written	0.90%	0.30%	0.30%
Direct - Premiums earned	$ 93,505	$ 85,213	$ 83,418
Assumed - Premium earned	713	259	275
Ceded - Premium earned	(45)	(51)	(45)
Premiums	$ 94,173	$ 85,421	$ 83,648
Percentage - assumed to net premiums - earned	0.80%	0.30%	0.30%