REGULATORY ASSETS, LIABILITIES, AND BALANCING ACCOUNTS (Long-Term Regulatory Liabilities) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	$ 8,607	$ 8,679
Cost of removal obligations
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	5,888	5,547
Deferred income taxes
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	437	1,021
Recoveries in excess of AROs
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	489	624
Public purpose programs
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	660	590
Other
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	$ 1,133	$ 897