Selected Quarterly Financial Data (Schedule Of Selected Quarterly Financial Data) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Selected Quarterly Financial Data [Abstract]
Operating revenue	$ 8,928	$ 10,171	$ 9,809	$ 8,202	$ 8,464	$ 5,417	$ 5,184	$ 4,260	$ 37,110	$ 23,325	$ 16,335
Income (loss) from operations	45	935	808	34	(82)	541	441	76	1,822	976	(161)
Net income (loss)	$ (138)	$ 653	$ 538	$ (213)	$ (325)	$ 387	$ 273	$ (82)	$ 840	$ 253	$ (651)
Basic earnings (loss) per share	$ (0.42)	$ 1.97	$ 1.63	$ (0.65)	$ (1.01)	$ 2.30	$ 1.62	$ (0.49)	$ 2.54	$ 1.22	$ (4.32)
Diluted earnings (loss) per share	$ (0.42)	$ 1.69	$ 1.39	$ (0.65)	$ (1.01)	$ 1.75	$ 1.29	$ (0.49)	$ 2.26	$ 1.08	$ (4.32)