Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Supplemental Cash Flow Information [Line Items]
Operating Lease, Payments	$ 271	$ 0
Interest paid	318	292
Income Taxes Paid, Net	9	12
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	183	0
Increase (decrease) in accounts payable for purchases of property and equipment	18	22
Purchase of property and equipment under capital leases and installment purchases	22	$ 17
Cash and cash equivalents	288		$ 277
Restricted Cash, Current	136		131
Restricted Cash, Noncurrent	5		5
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 429		$ 413