Taxation (Provision For Income Taxes) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Tax Disclosure [Abstract]
Current tax expense	$ 305	$ 485	$ 443
Deferred tax expense	(35)	17	110
Provision for income taxes	$ 270	$ 502	$ 553