Other Financial Information (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Prepaid Expenses and Other Current Assets [Abstract]
Prepaid expenses	$ 294	$ 290
Income tax receivable	15	7
Materials, supplies and inventory	103	105
Contract assets	49	66
Note receivable	56	0
Receivable for sale of land	56	0
Other	22	53
Total other current assets	843	808
Acquisition Costs
Prepaid Expenses and Other Current Assets [Abstract]
Contract costs	144	173
Fulfillment Costs
Prepaid Expenses and Other Current Assets [Abstract]
Contract costs	$ 104	$ 114