Property and Equipment - Depreciation Expense and Capitalized Interest (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Depreciation expense	$ 223	$ 251
Capitalized interest	$ 7	$ 1	$ 12	$ 3
Property, Plant and Equipment [Member]
Depreciation expense			$ 452	$ 515