Fair Value Measurements Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments	$ 14	$ 7
Derivatives, Assets	19	25
Derivatives, Liabilities	(258)	(217)
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	3,164	3,826
Available-for-sale investments	14	7
Derivatives, Assets	19	25
Total assets	3,197	3,858
Derivatives, Liabilities	(258)	(217)
Total liabilities	(258)	(217)
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	3,164	3,826
Available-for-sale investments	14	7
Total assets	3,178	3,833
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, Assets	19	25
Total assets	19	25
Derivatives, Liabilities	(258)	(217)
Total liabilities	$ (258)	$ (217)
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets