Other Financial Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Prepaid Expenses and Other Current Assets [Abstract]
Prepaid expenses	$ 274	$ 307
Income tax receivable	35	82
Materials, supplies and inventory	105	120
Contract assets	42	52
Contract acquisition costs	178	167
Other	59	108
Total other current assets	808	918
Accounts Payable, Current [Abstract]
Accounts payable	1,724	1,933
Other current liabilities:
Accrued rent	75	45
Legal contingencies	88	30
Other	223	282
Total other current liabilities	386	357
Book overdraft balance	106	86
Capital expenditures included in accounts payable	469	434
Contract Fulfillment Costs
Prepaid Expenses and Other Current Assets [Abstract]
Contract assets	$ 115	$ 82