COMMITMENTS AND CONTINGENCIES - OTHER LITIGATION (Details) £ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2015 GBP (£)	May 03, 2018 lawsuit	Mar. 31, 2018 USD ($) proof_of_claim lawsuit	Oct. 01, 2014 GBP (£)
Loss Contingencies [Line Items]
Investment in RBS Sempra Commodities LLP | $			$ 67
HMRC VAT Claim [Member]
Loss Contingencies [Line Items]
VAT tax claim paid upon appeal				£ 86
Filed claims amount	£ 160
Southern California Gas Company [Member] | Subsequent Event [Member] | Aliso Canyon Natural Gas Storage Facility Gas Leak [Member]
Loss Contingencies [Line Items]
Number of lawsuits | lawsuit		381
Plaintiffs [Member] | HMRC VAT Claim [Member]
Loss Contingencies [Line Items]
Filed claims amount	£ 80
Energy Future Holdings Corp. [Member]
Loss Contingencies [Line Items]
Number of lawsuits | lawsuit			140
Number of proof of claims | proof_of_claim			28,000