Variable Interest Entities - Balance Sheets Information (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Assets
Cash and cash equivalents	$ 730	$ 352
Accounts receivable	845	775
Other current assets	20	21
Licenses	2,189	2,223
Property, plant and equipment, net	2,126	2,320
Other assets and deferred charges	546	390
Liabilities
Current liabilities	689	733
Consolidated Variable Interest Entities
Assets
Cash and cash equivalents	24	3
Accounts receivable	584	476
Other current assets	8	8
Assets held for sale	2	0
Licenses	652	655
Property, plant and equipment, net	93	99
Other assets and deferred charges	325	303
Total assets	1,688	1,544
Liabilities
Current liabilities	31	39
Deferred liabilities and credits	15	13
Total liabilities	$ 46	$ 52