Property Casualty Loss And Loss Expenses (Consolidated Property Casualty Loss And Loss Expense Reserves) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Insurance [Abstract]
Gross loss and loss expense reserves, January 1	$ 5,219	$ 5,035	$ 4,660
Less reinsurance recoverable	187	298	281
Net loss and loss expense reserves, January 1	5,032	4,737	4,379
Net incurred loss and loss expenses related to:
Current accident year	3,390	3,257	3,029
Prior accident years	(167)	(119)	(168)
Total incurred	3,223	3,138	2,861
Net paid loss and loss expenses related to:
Current accident year	1,391	1,404	1,260
Prior accident years	1,456	1,439	1,243
Total paid	2,847	2,843	2,503
Net loss and loss expense reserves, December 31	5,408	5,032	4,737
Plus reinsurance recoverable	238	187	298
Gross loss and loss expense reserves, December 31	$ 5,646	$ 5,219	$ 5,035