REGULATORY ASSETS, LIABILITIES, AND BALANCING ACCOUNTS (Long-Term Regulatory Assets) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 4,121	$ 3,793
Pension benefits
Regulatory Assets [Line Items]
Total long-term regulatory assets	1,877	1,954
Environmental compliance costs
Regulatory Assets [Line Items]
Total long-term regulatory assets	784	837
Utility retained generation
Regulatory Assets [Line Items]
Total long-term regulatory assets	297	319
Price risk management
Regulatory Assets [Line Items]
Total long-term regulatory assets	63	65
Unamortized loss, net of gain, on reacquired debt
Regulatory Assets [Line Items]
Total long-term regulatory assets	84	79
Catastrophic event memorandum account
Regulatory Assets [Line Items]
Total long-term regulatory assets	654	274
Wildfire expense memorandum account
Regulatory Assets [Line Items]
Total long-term regulatory assets	69	0
Other
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 293	$ 265