Quarterly Financial Data (Unaudited) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Selected Quarterly Financial Information [Abstract]
Revenues	$ 8,602	$ 9,923	$ 9,732	$ 8,413	$ 8,399	$ 9,816	$ 9,153	$ 7,747	$ 36,670	$ 35,115	$ 31,755
Operating Income (Loss)	352	1,308	134	382	726	860	481	(92)	2,175	1,975	2,217
Net Income (Loss) Attributable to Parent	$ 7	$ 1,047	$ (168)	$ 124	$ 425	$ 549	$ 198	$ (318)	$ 1,009	$ 854	$ 593
Earnings Per Share, Basic	$ 0.01	$ 1.24	$ (0.20)	$ 0.15	$ 0.51	$ 0.66	$ 0.24	$ (0.38)	$ 1.20	$ 1.02	$ 0.71
Earnings Per Share, Diluted	$ 0.01	$ 1.23	$ (0.20)	$ 0.15	$ 0.50	$ 0.65	$ 0.23	$ (0.38)	$ 1.19	$ 1.01	$ 0.70