CONTINGENCIES AND COMMITMENTS (Regulatory Proceedings) (Details)	3 Months Ended
	Mar. 31, 2018 USD ($)
Potential Safety Citations
Loss Contingencies [Line Items]
Safety and enforcement division maximum statutory penalty per violation	$ 50,000
Safety and enforcement division administrative limit per citation	8,000,000
Potential Safety Citations | Minimum
Loss Contingencies [Line Items]
S E D fines for self reported violations	50,000
Potential Safety Citations | Maximum
Loss Contingencies [Line Items]
S E D fines for self reported violations	16,800,000
Ex Parte Communications
Loss Contingencies [Line Items]
Payment to State General Fund	12,000,000
Proposed penalty	97,500,000
Gas transmission and storage revenue reduction	63,500,000
2018 GTandS revenue requirement reduction	31,750,000
2019 GTandS revenue requirement reduction	31,750,000
Revenue requirement reduction in Next GRC cycle	10,000,000
Payment to city of San Bruno	6,000,000
Payment to city of San Carlos	6,000,000
Disallowance of Plant Costs
Loss Contingencies [Line Items]
Accrual for GTandS revenue requirement reduction	8,000,000
Payable to California General Fund and Cities of San Bruno and San Carlos
Loss Contingencies [Line Items]
Accrual for settlement payments	$ 24,000,000