Income Taxes - Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets
Deferred revenue	$ 298	$ 256
Net operating loss carry forwards	3,494	3,633
Property, plant and equipment	57	63
Other	309	282
Gross deferred tax assets	4,158	4,234
Less valuation allowance	(931)	(942)
Net deferred tax assets	3,227	3,292
Deferred tax liabilities
Deferred revenue	(45)	(44)
Property, plant and equipment	(853)	(689)
Intangible assets	(1,998)	(2,329)
Other	(25)	(16)
Gross deferred tax liabilities	(2,921)	(3,078)
Net deferred tax assets	$ 306	$ 214