Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Supplemental Cash Flow Information [Line Items]
Cash and cash equivalents	$ 323		$ 314
Interest paid	503	$ 420
Income taxes paid	15	14
Increase (decrease) in accounts payable for purchases of property and equipment	25	(5)
Purchase of property and equipment under capital leases and installment purchases	28	25
Restricted Cash, Current	125		121
Restricted Cash, Noncurrent	5		5
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	453		$ 440
Preferred Stock [Member]
Supplemental Cash Flow Information [Line Items]
Preferred Stock Dividends Declared, Not Paid	$ 0	$ 30