Supplementary Information for Certain Balance Sheet Accounts - Deferred Revenue and Accrued Expenses (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Accounts payable, accrued liabilities and deferred income	$ 793	$ 691
Accrued discretionary and incentive compensation	417	758
Accrued vacation	174	111
Other employee-related liabilities	60	87
Total deferred revenue and accrued expenses	$ 1,444	$ 1,647