Fair Value Measurements Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivatives	$ 23	$ 15
Derivatives	(202)	(305)
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Money market funds	2,858	4,504
Commercial Paper, at Carrying Value	162	87
Available-for-sale Securities, Debt Securities	271	79
Available for Sale Securities, Government Agencies	63	83
Available-for-sale Securities, Equity Securities	46	20
Derivatives	23	15
Total assets	3,423	4,788
Derivatives	(202)	(305)
Total liabilities	(202)	(305)
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Money market funds	2,858	4,504
Available-for-sale Securities, Equity Securities	46	20
Total assets	2,904	4,524
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Commercial Paper, at Carrying Value	162	87
Available-for-sale Securities, Debt Securities	271	79
Available for Sale Securities, Government Agencies	63	83
Derivatives	23	15
Total assets	519	264
Derivatives	(202)	(305)
Total liabilities	$ (202)	$ (305)