Fair Value Measurements Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	$ 3,569	$ 4,534
Available-for-sale investments	9	9
Derivatives, Assets	150	178
Total assets	3,728	4,721
Derivatives, Liabilities	(88)	(84)
Total liabilities	(88)	(84)
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	3,569	4,534
Available-for-sale investments	6	6
Total assets	3,575	4,540
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, Assets	150	178
Total assets	150	178
Derivatives, Liabilities	(88)	(84)
Total liabilities	(88)	(84)
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments	3	3
Total assets	$ 3	$ 3