Property Casualty Loss And Loss Expenses (Consolidated Property Casualty Loss And Loss Expense Reserves) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Insurance [Abstract]
Gross loss and loss expense reserves, January 1	$ 4,660	$ 4,438	$ 4,241
Less reinsurance recoverable	281	282	299
Net loss and loss expense reserves, January 1	4,379	4,156	3,942
Net incurred loss and loss expenses related to:
Current accident year	3,029	2,756	2,725
Prior accident years	(168)	(184)	(98)
Total incurred	2,861	2,572	2,627
Net paid loss and loss expenses related to:
Current accident year	1,260	1,152	1,212
Prior accident years	1,243	1,197	1,201
Total paid	2,503	2,349	2,413
Net loss and loss expense reserves, December 31	4,737	4,379	4,156
Plus reinsurance recoverable	298	281	282
Gross loss and loss expense reserves, December 31	$ 5,035	$ 4,660	$ 4,438