Fair Value Measurements (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	$ 266	$ 249
Derivatives	86	208
Total Assets at Fair Value	352	457
Derivatives	149	102
Total Liabilities at Fair Value	149	102
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	266	249
Derivatives	21	104
Total Assets at Fair Value	287	353
Derivatives	148	101
Total Liabilities at Fair Value	148	101
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	0	0
Derivatives	65	104
Total Assets at Fair Value	65	104
Derivatives	1	1
Total Liabilities at Fair Value	1	1
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	0	0
Derivatives	0	0
Total Assets at Fair Value	0	0
Derivatives	0	0
Total Liabilities at Fair Value	$ 0	$ 0