Unpaid Losses And Loss Expenses (A&E Loss Roll-Forward) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011
Unpaid Losses And Loss Expenses [Line Items]
A&E loss reserves, gross - opening	$ 2,446
A&E gross - incurred activity	214
A&E gross - Payment activity	(410)
A&E loss reserves, gross - closing	2,250
A&E loss reserves, net - opening	1,335
A&E net - incurred activity	104
A&E net - Payment activity	(243)
A&E loss reserves, net - closing	1,196
Asbestos Issue [Member]
Unpaid Losses And Loss Expenses [Line Items]
A&E loss reserves, gross - opening	2,130
A&E gross - incurred activity	148
A&E gross - Payment activity	(311)
A&E loss reserves, gross - closing	1,967
A&E loss reserves, net - opening	1,120
A&E net - incurred activity	67
A&E net - Payment activity	(168)
A&E loss reserves, net - closing	1,019
Environmental Issue [Member]
Unpaid Losses And Loss Expenses [Line Items]
A&E loss reserves, gross - opening	316
A&E gross - incurred activity	66
A&E gross - Payment activity	(99)
A&E loss reserves, gross - closing	283
A&E loss reserves, net - opening	215
A&E net - incurred activity	37
A&E net - Payment activity	(75)
A&E loss reserves, net - closing	$ 177