Fair Value Measurements Fair Value Tables of Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Millions	Sep. 30, 2018		Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	$ 55		$ 46
Derivative Liability	54		79
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents and Restricted Cash Equivalents	2,641	[1]	5,205	[2]
Marketable Securities	264		952
Assets at Fair Value	2,960		6,203
Long-term Debt, Fair Value	10,388		11,560
Liabilities at Fair Value	10,442		11,639
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Foreign Exchange Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	55	[3]	46	[4]
Derivative Liability	$ 54	[3]	$ 79	[4]

[1] Time deposits included in cash and cash equivalents and money market funds included in other current assets in the interim Condensed Consolidated Balance Sheets are held at amortized cost, which approximates fair value.

[2] Time deposits included in cash and cash equivalents and money market funds included in other current assets in the interim Condensed Consolidated Balance Sheets are held at amortized cost, which approximates fair value.

[3] See Note 17 for the classification of derivatives in the interim Condensed Consolidated Balance Sheets.

[4] See Note 17 for the classification of derivatives in the interim Condensed Consolidated Balance Sheets.