Other Financial Information (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Prepaid Expenses and Other Current Assets [Abstract]
Prepaid expenses	$ 352	$ 307
Income tax receivable	5	82
Materials, supplies and inventory	137	120
Contract assets	51	52
Other	53	108
Total other current assets	884	918
Contract Acquisition Costs
Prepaid Expenses and Other Current Assets [Abstract]
Contract costs	175	167
Contract Fulfillment Costs
Prepaid Expenses and Other Current Assets [Abstract]
Contract costs	$ 111	$ 82