COMMITMENTS AND CONTINGENCIES - NUCLEAR INSURANCE (Details) - San Diego Gas and Electric Company [Member] $ in Millions	Sep. 30, 2017 USD ($)
Schedule Of Nuclear Insurance [Line Items]
Maximum nuclear liability insurance coverage	$ 450.0
Maximum secondary financial protection	13,000.0
Maximum company contribution to secondary financial protection	50.9
Annual maximum secondary financial protection contribution by company	7.6
Federal nuclear property damage insurance, minimum required	1,060.0
Maximum premium assessment under nuclear property damage insurance	10.4
Maximum nuclear property insurance terrorism coverage	$ 3,240.0