REGULATORY ASSETS, LIABILITIES, AND BALANCING ACCOUNTS (Long-Term Regulatory Liabilities) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	$ 8,498	$ 8,679
Cost of removal obligations
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	5,775	5,547
Deferred income taxes
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	611	1,021
Recoveries in excess of AROs
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	467	624
Public purpose programs
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	636	590
Other
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	$ 1,009	$ 897