Fair Value Measurements Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments	$ 8	$ 9
Derivatives, Assets	120	178
Derivatives, Liabilities	(83)	(84)
Fair Value, Measurements, Recurring [Member] | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	4,744	4,534
Available-for-sale investments	8	9
Derivatives, Assets	120	178
Total assets	4,872	4,721
Derivatives, Liabilities	(83)	(84)
Total liabilities	(83)	(84)
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	4,744	4,534
Available-for-sale investments	6	6
Total assets	4,750	4,540
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, Assets	120	178
Total assets	120	178
Derivatives, Liabilities	(83)	(84)
Total liabilities	(83)	(84)
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments	2	3
Total assets	$ 2	$ 3