EMPLOYEE BENEFIT PLANS (Additional Information) (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) plan	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Number of defined benefit pension plans | plan	3
Number of qualified defined benefit pension plans | plan	2
Approximate percentage of net periodic benefit cost that was capitalized	18.00%	18.00%	18.00%
Investment Return Model Best-Estimate Range	20 years
Matching 401(k) contributions made	$ 6,000,000	$ 5,000,000	$ 5,000,000
Level 3
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value measurements of plan assets	27,000,000	26,000,000	25,000,000
Pension Benefits
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Accumulated benefit obligation	428,000,000	384,000,000
Fair value measurements of plan assets	403,000,000	354,000,000	336,000,000
Pension Benefits | Level 3
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value measurements of plan assets	27,000,000	26,000,000
Transfers between levels	0	0
Other Postretirement Benefits
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Employer Contribution to VEBA Trust	3,000,000	2,000,000	4,000,000
Fair value measurements of plan assets	17,000,000	14,000,000	$ 13,000,000
Other Postretirement Benefits | FairValueInputsLevel1AndLevel2
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value measurements of plan assets	17,000,000	14,000,000
Other Postretirement Benefits | Level 3
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value measurements of plan assets	$ 0	0
Minimum
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Percentile of investment return model range used	25.00%
Maximum
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Percentile of investment return model range used	75.00%
Fixed Income Securities | Pension Benefits
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value measurements of plan assets	$ 179,000,000	144,000,000
Fixed Income Securities | Pension Benefits | Level 3
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value measurements of plan assets	0	0
Fixed Income Securities | Other Postretirement Benefits | FairValueInputsLevel1AndLevel2
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value measurements of plan assets	6,000,000	5,000,000
Equities | Other Postretirement Benefits | FairValueInputsLevel1AndLevel2
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value measurements of plan assets	$ 11,000,000	$ 9,000,000