Summary of Significant Accounting Policies and Other Matters - Long-Lived and Intangible Assets (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019 USD ($) MW	Dec. 31, 2018 USD ($)
Finite-Lived Intangible Assets [Line Items]
Net non-utility plant	$ 43,234	$ 41,749
Intangible assets	1,580	$ 1,654
PG&E Project
Finite-Lived Intangible Assets [Line Items]
Net non-utility plant	827
Intangible assets	1,075
Long-term debt	1,012
PG&E Project | Secured Related to Project Debt
Finite-Lived Intangible Assets [Line Items]
Net non-utility plant	$ 287
Con Edison Development | PG&E Project
Finite-Lived Intangible Assets [Line Items]
Aggregate power to be sold (in MW) | MW	680