Reinsurance Reinsurance (Written Consolidated Property Casualty Insurance Premiums On Assumed and Ceded Business) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
SEC Schedule, 12-17, Insurance Companies, Reinsurance
Direct premiums earned	$ 7,050	$ 6,370	$ 5,985
Assumed premiums earned	561	443	285
Ceded premiums earned	(392)	(331)	(290)
Incurred loss and loss expenses	5,012	3,936	4,134
Consolidated Property And Casualty Insurance Entity
SEC Schedule, 12-17, Insurance Companies, Reinsurance
Direct premiums written	7,002	6,229	5,756
Assumed premiums written	619	515	335
Ceded premiums written	(314)	(265)	(227)
Net written premiums	7,307	6,479	5,864
Direct premiums earned	6,677	5,996	5,623
Assumed premiums earned	561	443	285
Ceded premiums earned	(314)	(255)	(217)
Earned premiums	6,924	6,184	5,691
Direct incurred loss and loss expenses	4,495	3,352	3,699
Assumed incurred loss and loss expenses	396	366	184
Ceded incurred loss and loss expenses	(175)	(122)	(46)
Incurred loss and loss expenses	$ 4,716	$ 3,596	$ 3,837