Quarterly Financial Data (Unaudited) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Selected Quarterly Financial Information [Abstract]
Total Operating Revenue	$ 9,076	$ 10,490	$ 9,707	$ 8,500	$ 8,602	$ 9,923	$ 9,732	$ 8,413	$ 37,773	$ 36,670	$ 35,115
Operating Income (Loss)	701	1,563	914	222	352	1,308	134	382	3,400	2,175	1,975
Net Income	$ 8,479	$ 1,369	$ 685	$ 7	$ 7	$ 1,047	$ (168)	$ 124	$ 10,540	$ 1,009	$ 854
Basic earnings per share	$ 10.02	$ 1.61	$ 0.81	$ 0.01	$ 0.01	$ 1.24	$ (0.20)	$ 0.15	$ 12.41	$ 1.20	$ 1.02
Diluted earnings per share	$ 9.89	$ 1.59	$ 0.80	$ 0.01	$ 0.01	$ 1.23	$ (0.20)	$ 0.15	$ 12.29	$ 1.19	$ 1.01