Fair Value Measurements Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) (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]
Money market funds	$ 4,534	$ 3,104
Available-for-sale investments	9	10
Derivatives	178	155
Total assets	4,721	3,269
Derivatives	(84)	(131)
Total liabilities	(84)	(131)
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	4,534	3,104
Available-for-sale investments	6	5
Total assets	4,540	3,109
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives	178	155
Total assets	178	155
Derivatives	(84)	(131)
Total liabilities	(84)	(131)
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments	3	5
Total assets	$ 3	$ 5