Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Supplemental Cash Flow Information [Line Items]
Cash and cash equivalents	$ 206		$ 314
Interest paid	292	$ 260
Income taxes paid	12	10
Increase (decrease) in accounts payable for purchases of property and equipment	22	(8)
Purchase of property and equipment under capital leases and installment purchases	17	18
Restricted Cash, Current	125		121
Restricted Cash, Noncurrent	5		5
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	336		$ 440
Preferred Stock [Member]
Supplemental Cash Flow Information [Line Items]
Preferred Stock Dividends Declared, Not Paid	$ 28	$ 0