REGULATORY ASSETS, LIABILITIES, AND BALANCING ACCOUNTS (Long-Term Regulatory Assets) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 3,724	$ 3,793
Pension benefits
Regulatory Assets [Line Items]
Total long-term regulatory assets	1,915	1,954
Environmental compliance costs
Regulatory Assets [Line Items]
Total long-term regulatory assets	749	837
Utility retained generation
Regulatory Assets [Line Items]
Total long-term regulatory assets	308	319
Price risk management
Regulatory Assets [Line Items]
Total long-term regulatory assets	68	65
Unamortized loss, net of gain, on reacquired debt
Regulatory Assets [Line Items]
Total long-term regulatory assets	88	79
Catastrophic event memorandum account
Regulatory Assets [Line Items]
Total long-term regulatory assets	314	274
Other
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 282	$ 265