Fair Value Measurements Summary of Classification of Equity Investment in Galapagos on Balance Sheet (Details) - Equity investment in Galapagos - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total	$ 2,082	$ 622
Prepaid and other current assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Equity securities	0	622
Other long-term assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Equity securities	$ 2,082	$ 0