Other Financial Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Prepaid Expenses and Other Current Assets [Abstract]
Prepaid expenses	$ 307	$ 294
Income tax receivable	82	258
Materials, supplies and inventory	120	128
Contract assets	134	0
Contract acquisition costs and deferred activation and installation charges	167	128
Other	108	133
Total other current assets	918	941
Accounts Payable, Current [Abstract]
Accounts payable	1,933	1,555
Other current liabilities:
Accrued rent	45	34
Legal contingencies	30	45
Other	282	265
Total other current liabilities	357	344
Book overdraft balance	86	36
Capital expenditures included in accounts payable	$ 434	$ 225