Reinsurance Reinsurance (Written Consolidated Property Casualty Insurance Premiums On Assumed and Ceded Business) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
SEC Schedule, 12-17, Insurance Companies, Reinsurance
Direct premiums earned	$ 6,370	$ 5,985	$ 5,681
Assumed premiums earned	443	285	199
Ceded premiums earned	(331)	(290)	(276)
Incurred loss and loss expenses	3,936	4,134	3,638
Consolidated Property And Casualty Insurance Entity
SEC Schedule, 12-17, Insurance Companies, Reinsurance
Direct premiums written	6,229	5,756	5,477
Assumed premiums written	515	335	244
Ceded premiums written	(265)	(227)	(205)
Net written premiums	6,479	5,864	5,516
Direct premiums earned	5,996	5,623	5,340
Assumed premiums earned	443	285	199
Ceded premiums earned	(255)	(217)	(205)
Earned premiums	6,184	5,691	5,334
Direct incurred loss and loss expenses	3,352	3,699	3,402
Assumed incurred loss and loss expenses	366	184	117
Ceded incurred loss and loss expenses	(122)	(46)	(167)
Incurred loss and loss expenses	$ 3,596	$ 3,837	$ 3,352