REGULATORY ASSETS, LIABILITIES, AND BALANCING ACCOUNTS (Long-Term Regulatory Assets) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 4,429	$ 3,793
Pension benefits
Regulatory Assets [Line Items]
Total long-term regulatory assets	1,837	1,954
Environmental compliance costs
Regulatory Assets [Line Items]
Total long-term regulatory assets	851	837
Utility retained generation
Regulatory Assets [Line Items]
Total long-term regulatory assets	285	319
Price risk management
Regulatory Assets [Line Items]
Total long-term regulatory assets	67	65
Unamortized loss, net of gain, on reacquired debt
Regulatory Assets [Line Items]
Total long-term regulatory assets	80	79
Catastrophic event memorandum account
Regulatory Assets [Line Items]
Total long-term regulatory assets	760	274
Wildfire expense memorandum account
Regulatory Assets [Line Items]
Total long-term regulatory assets	77	0
Fire hazard prevention memorandum account
Regulatory Assets [Line Items]
Total long-term regulatory assets	65	1
Other
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 407	$ 264