Other Financial Information (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Prepaid Expenses and Other Current Assets [Abstract]
Prepaid expenses	$ 312	$ 274
Income tax receivable	6	35
Materials, supplies and inventory	112	105
Contract assets	35	42
Other	81	70
Total other current assets	835	819
Acquisition Costs
Prepaid Expenses and Other Current Assets [Abstract]
Contract costs	172	178
Fulfillment Costs
Prepaid Expenses and Other Current Assets [Abstract]
Contract costs	$ 117	$ 115