CONDENSED CONSOLIDATING FINANCIAL INFORMATION - Balance sheet (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Assets
Total current assets	$ 452	$ 425
Total property, plant and equipment, net	5,692	5,885
Other assets	39	44
TOTAL ASSETS	6,183	6,354
Total current liabilities	746	726
Long-Term Debt - Principal Amount	5,039	5,168
Deferred gain and issuance costs, net	356	397
Other long-term liabilities	616	620
Total equity	(574)	(557)
TOTAL LIABILITIES AND EQUITY	6,183	6,354
Eliminations
Assets
Total current assets	(2)
Investments in consolidated subsidiaries	(6,563)	(6,250)
TOTAL ASSETS	(6,565)	(6,250)
Total current liabilities	(2)
Total equity	(6,563)	(6,250)
TOTAL LIABILITIES AND EQUITY	(6,565)	(6,250)
Parent | Reportable Legal Entity
Assets
Total current assets	9	7
Total property, plant and equipment, net	24	25
Investments in consolidated subsidiaries	5,981	5,713
TOTAL ASSETS	6,014	5,745
Total current liabilities	234	221
Long-Term Debt - Principal Amount	5,039	5,168
Deferred gain and issuance costs, net	356	397
Other long-term liabilities	138	132
Amounts due to (from) affiliates	914	384
Total equity	(667)	(557)
TOTAL LIABILITIES AND EQUITY	6,014	5,745
Combined Guarantor Subsidiaries | Reportable Legal Entity
Assets
Total current assets	425	418
Total property, plant and equipment, net	5,589	5,856
Investments in consolidated subsidiaries	582	537
Other assets	37	44
TOTAL ASSETS	6,633	6,855
Total current liabilities	513	505
Other long-term liabilities	475	487
Amounts due to (from) affiliates	(914)	(384)
Total equity	6,559	6,247
TOTAL LIABILITIES AND EQUITY	6,633	6,855
Combined Non-Guarantor Subsidiaries | Reportable Legal Entity
Assets
Total current assets	20
Total property, plant and equipment, net	79	4
Other assets	2
TOTAL ASSETS	101	4
Total current liabilities	1
Other long-term liabilities	3	1
Total equity	97	3
TOTAL LIABILITIES AND EQUITY	$ 101	$ 4