Fair Value Measurements (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable Securities	$ 239	$ 249
Derivatives	192	208
Total Assets at Fair Value	431	457
Derivatives	128	102
Total Liabilities at Fair Value	128	102
Level 1 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable Securities	239	249
Derivatives	90	104
Total Assets at Fair Value	329	353
Derivatives	117	101
Total Liabilities at Fair Value	117	101
Level 2 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable Securities
Derivatives	102	104
Total Assets at Fair Value	102	104
Derivatives	11	1
Total Liabilities at Fair Value	11	1
Level 3 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable Securities
Derivatives
Total Assets at Fair Value
Derivatives
Total Liabilities at Fair Value