SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Asset Retirement Obligation (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Public Utility, Property, Plant and Equipment [Line Items]
Asset retirement obligation	$ 5,512	$ 5,512	$ 5,912	$ 5,298
Revision in estimated cash flows		(585)	325
Decrease in decommissioning cost		253
Pacific Gas & Electric Co (Utility)
Public Utility, Property, Plant and Equipment [Line Items]
Asset retirement obligation	5,500	5,500	5,900
Revision in estimated cash flows	$ (205)
Nuclear decommissioning obligation accrued		$ 4,000	$ 4,100