Fair Value Measurements Summary of Classification of Other Equity Securities on Balance Sheet (Details) - Other Equity Securities - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total	$ 4,054	$ 5,688
Cash and cash equivalents
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Equity securities	3,599	5,305
Prepaid and other current assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Equity securities	292	241
Other long-term assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Equity securities	$ 163	$ 142