Fair Value Measurements Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments	$ 9	$ 7
Derivatives, Assets	24	25
Derivatives, Liabilities	(332)	(217)
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	3,134	3,826
Available-for-sale investments	9	7
Derivatives, Assets	24	25
Total assets	3,167	3,858
Derivatives, Liabilities	(332)	(217)
Total liabilities	(332)	(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	3,134	3,826
Available-for-sale investments	9	7
Total assets	3,143	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	24	25
Total assets	24	25
Derivatives, Liabilities	(332)	(217)
Total liabilities	(332)	(217)
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
Total assets