Other Financial Information (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Prepaid Expenses and Other Current Assets [Abstract]
Prepaid expenses	$ 403	$ 290
Income tax receivable	6	7
Materials, supplies and inventory	100	105
Contract assets	64	66
Other	66	53
Total other current assets	924	808
Acquisition Costs
Prepaid Expenses and Other Current Assets [Abstract]
Contract costs	170	173
Fulfillment Costs
Prepaid Expenses and Other Current Assets [Abstract]
Contract costs	$ 115	$ 114