Fair Value Measurements Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments	$ 11	$ 8
Derivatives, Assets	88	86
Derivatives, Liabilities	(87)	(79)
Fair Value, Measurements, Recurring [Member] | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	2,101	3,783
Available-for-sale investments	11	8
Derivatives, Assets	88	86
Total assets	2,200	3,877
Derivatives, Liabilities	(87)	(79)
Total liabilities	(87)	(79)
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	2,101	3,783
Available-for-sale investments	9	6
Total assets	2,110	3,789
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, Assets	88	86
Total assets	88	86
Derivatives, Liabilities	(87)	(79)
Total liabilities	(87)	(79)
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	2
Total assets	$ 2	$ 2