Other Financial Information (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Prepaid Expenses and Other Current Assets [Abstract]
Prepaid expenses	$ 379	$ 294
Income tax receivable	79	258
Materials, supplies and inventory	131	128
Contract assets	359	128
Contract acquisition costs	155	0
Other	134	133
Total other current assets	1,237	941
Other Current Liabilities
Accrued contributions to federal programs	136	74
Dividends payable	51	34
Accrued rents	41	14
Accrued rents-telephone poles	35	34
Litigation contingencies	31	45
Other	80	143
Total other current liabilities	374	344
Accounts Payable, Current [Abstract]
Book overdraft balance	$ 58	$ 36