Other Financial Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Jan. 22, 2018
Prepaid Expenses and Other Current Assets [Abstract]
Prepaid expenses	$ 294	$ 206
Income tax receivable	258	51
Materials, supplies and inventory	128	134
Deferred activation and installation charges	128	101
Other	133	55
Total other current assets	941	547
Accounts Payable, Current [Abstract]
Accounts payable	1,555	1,179
Other current liabilities:
Accrued rent	34	31
Legal contingencies	45	30
Other	265	152
Total other current liabilities	344	213
Book overdraft balance	36	56
Capital expenditures included in accounts payable	$ 225	$ 196
Subsequent event
Subsequent Event [Line Items]
Assets Held-for-sale, Not Part of Disposal Group, Current			$ 68