Fair Value Measurements Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, Assets	$ 81	$ 23
Derivatives, Liabilities	(21)	(202)
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	2,042	2,858
Commercial Paper, at Carrying Value	59	162
Available-for-sale Securities, Debt Securities	392	271
Available for Sale Securities, Government Agencies	47	63
Available-for-sale Securities, Equity Securities	15	46
Derivatives, Assets	81	23
Total assets	2,636	3,423
Derivatives, Liabilities	(21)	(202)
Total liabilities	(21)	(202)
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	2,042	2,858
Available-for-sale Securities, Equity Securities	15	46
Total assets	2,057	2,904
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Paper, at Carrying Value	59	162
Available-for-sale Securities, Debt Securities	392	271
Available for Sale Securities, Government Agencies	47	63
Derivatives, Assets	81	23
Total assets	579	519
Derivatives, Liabilities	(21)	(202)
Total liabilities	$ (21)	$ (202)