Fair Value Measurements (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities	$ 249	$ 155
Derivatives	208	122
Total Assets at Fair Value	457	277
Derivatives	102	171
Total Liabilities at Fair Value	102	171
Level 1 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities	249	155
Derivatives	104	11
Total Assets at Fair Value	353	166
Derivatives	101	75
Total Liabilities at Fair Value	101	75
Level 2 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities	0	0
Derivatives	104	111
Total Assets at Fair Value	104	111
Derivatives	1	96
Total Liabilities at Fair Value	1	96
Level 3 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities	0	0
Derivatives	0	0
Total Assets at Fair Value	0	0
Derivatives	0	0
Total Liabilities at Fair Value	$ 0	$ 0