REGULATORY MATTERS Additional Information (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2017	Dec. 31, 2016
Schedule of Regulatory Matters
Current regulatory assets	$ 27	$ 53
Transmission rate, applicable period	1 year
Revenue true-up amount reflected in customer bill, period of recognition	2 years
Regional Cost Allocation Refund
Schedule of Regulatory Matters
Current regulatory assets	$ 7	$ 29

Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 340
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382

Name:	us-gaap_RegulatoryAssetsCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant