LONG-TERM DEBT - SCHEDULE OF LONG-TERM DEBT (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term Debt	$ 2,569	$ 2,964
Less debt issuance costs	(15)	(18)
Less current portion	307	319
Long-term debt, net of current portion	$ 2,262	$ 2,645
Weighted-average fixed-interest rate	4.20%	4.40%
Weighted-average variable-interest rate	2.80%	2.40%
Proceeds from issuance of long-term debt, net of issuance costs	$ 0	$ 2,044	$ 0
Long-term debt payments	397	249	$ 116
Repayments of debt	74
Long-term Debt, Fiscal Year Maturity [Abstract]
2018	310
2019	393
2020	449
2021	414
2022	247
Thereafter	768
Long-term Debt	2,581
Fixed-rate notes payable due through 2028
Debt Instrument [Line Items]
Long-term Debt	959	1,179
Variable-rate notes payable due through 2028
Debt Instrument [Line Items]
Long-term Debt	$ 1,625	$ 1,803