Other Financial Information (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Prepaid Expenses and Other Current Assets [Abstract]
Prepaid expenses	$ 247	$ 206
Materials, supplies and inventory	144	134
Deferred activation and installation charges	105	101
Other	195	106
Total other current assets	691	547
Accounts Payable, Current [Abstract]
Accounts payable	944	1,179
Book overdraft balance	51	56
Capital expenditures incurred but not yet paid	73	196
Other Current Liabilities
Accrued rent	30	31
Legal contingencies	26	30
Other	182	152
Total other current liabilities	$ 238	$ 213