Fair Value Measurements Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	$ 3,411	$ 4,534
Available-for-sale investments	7	9
Derivatives, Assets	93	178
Total assets	3,511	4,721
Derivatives, Liabilities	(112)	(84)
Total liabilities	(112)	(84)
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	3,411	4,534
Available-for-sale investments	5	6
Total assets	3,416	4,540
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, Assets	93	178
Total assets	93	178
Derivatives, Liabilities	(112)	(84)
Total liabilities	(112)	(84)
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