Variable Interest Entities - Consolidataed Balance Sheet (Details) - USD ($) $ in Millions	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Assets
Cash and cash equivalents	$ 648		$ 580
Short-term investments	17		17
Accounts receivable	882		908
Inventory, net	157		142
Other current assets	29		34
Licenses	2,213		2,186
Property, plant and equipment, net	2,137		2,202
Operating lease right-of-use assets	888	$ 899	0
Other assets and deferred charges	684	567	579
Liabilities
Current liabilities	802		691
Liabilities held for sale	0		1
Long-term operating lease liabilities	858	$ 878	0
Consolidated Variable Interest Entities
Assets
Cash and cash equivalents	8		9
Short-term investments	17		17
Accounts receivable	619		611
Inventory, net	4		5
Other current assets	5		6
Assets held for sale	0		4
Licenses	652		652
Property, plant and equipment, net	92		94
Operating lease right-of-use assets	39		0
Other assets and deferred charges	339		349
Total assets	1,775		1,747
Liabilities
Current liabilities	37		34
Liabilities held for sale	0		1
Long-term operating lease liabilities	36		0
Deferred liabilities and credits	12		16
Total liabilities	$ 85		$ 51