Other Financial Information (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Prepaid Expenses and Other Current Assets [Abstract]
Prepaid expenses	$ 272	$ 206
Materials, supplies and inventory	138	134
Deferred activation and installation charges	105	101
Other	42	106
Total other current assets	557	547
Accounts Payable, Current [Abstract]
Accounts payable	994	1,179
Book overdraft balance	41	56
Capital expenditures incurred but not yet paid	93	196
Other Current Liabilities
Accrued rent	28	31
Legal contingencies	25	30
Other	124	152
Total other current liabilities	$ 177	$ 213