SEGMENT AND RELATED INFORMATION - Electric Utilities' Revenues (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue from External Customer [Line Items]
Total operating revenues	$ 21,419	$ 23,495	$ 23,031
Retail electric revenues
Revenue from External Customer [Line Items]
Total operating revenues	14,084	15,222	15,330
Other electric revenues
Revenue from External Customer [Line Items]
Total operating revenues	636	664	681
Electric Utilities
Revenue from External Customer [Line Items]
Total operating revenues	17,095	18,571	18,540
Electric Utilities | Retail electric revenues
Revenue from External Customer [Line Items]
Total operating revenues	14,084	15,222	15,330
Electric Utilities | Wholesale
Revenue from External Customer [Line Items]
Total operating revenues	2,152	2,516	2,426
Electric Utilities | Other electric revenues
Revenue from External Customer [Line Items]
Total operating revenues	$ 859	$ 833	$ 784