CONTINGENCIES AND COMMITMENTS (Schedule of Insurance Receivable) (Details) - Butte Fire - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Insurance Receivable [Roll Forward]
Insurance Receivable, Beginning Balance	$ 596	$ 575	$ 0
Accrued insurance recoveries	0	297	625
Reimbursements	(197)	(276)	(50)
Insurance Receivable, Ending Balance	$ 399	$ 596	$ 575

The increase (decrease) during the reporting period in insurance settlements receivable, which are amounts due in settlement of a claim for reimbursement from an insurance company when the Company has suffered a loss covered under an insurance policy. The expectation is that such reimbursement will be received within one year of the balance sheet date.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

Name:	us-gaap_IncreaseDecreaseInInsuranceSettlementsReceivable
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration