Unpaid Losses And Loss Expenses (Unpaid Losses And Loss Expenses Roll-Forward) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Unpaid Losses And Loss Expenses [Abstract]
Gross unpaid losses and loss expenses, beginning of the year	$ 37,391		$ 37,783		$ 37,176
Reinsurance recoverable on unpaid losses, beginning of the year	(12,149)	[1]	(12,745)	[1]	(12,935)	[1]
Net unpaid losses and loss expenses, beginning of year	25,242		25,038		24,241
Acquisition of subsidiaries	92		145
Net unpaid losses and loss expenses, Adjusted	25,334		25,183		24,241
Net losses and loss expenses incurred, Current year	10,076		8,082		7,998
Net losses and loss expenses incurred, Prior years	(556)		(503)		(576)
Net losses and loss expenses incurred, Total	9,520		7,579		7,422
Net losses and loss expenses paid, Current year	4,209		2,689		2,493
Net losses and loss expenses paid, Prior years	4,657		4,724		4,455
Net losses and loss expenses paid, Total	8,866		7,413		6,948
Foreign currency revaluation and other	(113)		(107)		323
Net unpaid losses and loss expenses, end of year	25,875		25,242		25,038
Reinsurance recoverable on unpaid losses, end of the year	11,602		12,149	[1]	12,745	[1]
Gross unpaid losses and loss expenses, end of the year	$ 37,477		$ 37,391		$ 37,783

[1] Net of provision for uncollectible reinsurance.