Other Financial Information (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Prepaid Expenses and Other Current Assets [Abstract]
Prepaid expenses	$ 371	$ 307
Income tax receivable	87	82
Materials, supplies and inventory	151	120
Contract assets	57	52
Other	66	108
Total other current assets	1,011	918
Contract Acquisition Costs
Prepaid Expenses and Other Current Assets [Abstract]
Contract costs	174	167
Contract Fulfillment Costs
Prepaid Expenses and Other Current Assets [Abstract]
Contract costs	$ 105	$ 82