Accumulated Other Comprehensive Loss (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated Other Comprehensive Loss, Pension and Other Benefit Liabilities	$ (5,111)	$ (3,814)	$ (5,147)	$ (3,899)
Accumulated Other Comprehensive Loss, Derivative Contracts	(228)	(344)	(286)	(413)
Accumulated Other Comprehensive Loss, Deferred Tax Impact	(3,087)	(2,360)	(3,144)	(2,454)
Accumulated other comprehensive loss	(8,426)	(6,518)	(8,577)	(6,766)
Pension and other benefits liabilities, changes in value	0	91
Derivative contracts, changes in value	114	116
Deferred tax impact, changes in value	0	0
Accumulated Other Comprehensive Loss, Changes In Value	114	207
Pension and Other Benefit Liabilities, reclassifications into earnings	58	41
Derivative contracts, reclassifications into earnings	(21)	0
Deferred tax impact, reclassifications into earnings	0	0
Accumulated Other Comprehensive Loss, Reclassifications into earnings	37	41
Pension and other benefit liabilities, tax effect	(22)	(47)
Derivative contracts, tax effect	(35)	(47)
Deferred tax impact, tax effect	57	94
Other Comprehensive Loss, Tax Effect	$ 0	$ 0