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	$ 9,005	$ 8,763	$ 8,843	$ 8,734	$ 8,722		$ 8,333		$ 8,311		$ 8,313		$ 35,345	$ 33,679	$ 32,563
Operating Income (Loss)	(705)	(231)	(629)	(255)	(438)		208		79		259		(1,820)	108	(595)
Net loss	$ (1,322)	$ (767)	$ (1,374)	$ (863)	$ (1,303)		$ (301)		$ (847)		$ (439)		$ (4,326)	$ (2,890)	$ (3,465)
Basic and diluted loss per common share	$ (0.44)	$ (0.26)	$ (0.46)	$ (0.29)	$ (0.43)	[1]	$ (0.10)	[1]	$ (0.28)	[1]	$ (0.15)	[1]	$ (1.44)	$ (0.96)	$ (1.16)

[1] (1)The sum of the quarterly earnings per share amounts may not equal the annual amounts because of the changes in the weighted average number of shares outstanding during the year.