Fair Value Measurements Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, Assets	$ 7	$ 28
Derivatives, Liabilities	(196)	(112)
Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	1,371	1,737
Commercial Paper, at Carrying Value	146	78
Available for sale debt instruments	352	420
Available for Sale Securities, Government Agencies	109
Investments, Fair Value Disclosure	10	12
Derivatives, Assets	7	28
Total assets	1,995	2,275
Derivatives, Liabilities	(196)	(112)
Total liabilities	(196)	(112)
Fair Value, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	1,371	1,737
Available for Sale Securities, Government Agencies	109
Investments, Fair Value Disclosure	10	12
Total assets	1,490	1,749
Fair Value, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Paper, at Carrying Value	146	78
Available for sale debt instruments	352	420
Derivatives, Assets	7	28
Total assets	505	526
Derivatives, Liabilities	(196)	(112)
Total liabilities	$ (196)	$ (112)