REGULATORY ASSETS, LIABILITIES, AND BALANCING ACCOUNTS (Long-Term Regulatory Liabilities) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	$ 8,586	$ 8,679
Cost of removal obligations
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	5,674	5,547
Deferred income taxes
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	873	1,021
Recoveries in excess of AROs
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	533	624
Public purpose programs
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	591	590
Other
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	$ 915	$ 897