Summary of Significant Accounting Policies and Other Matters - Long-Lived and Intangible Assets (Details) $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($) MW	Dec. 31, 2018 USD ($)
Finite-Lived Intangible Assets [Line Items]
Net non-utility plant	$ 42,745	$ 41,749
Intangible assets	1,605	$ 1,654
PG&E Project
Finite-Lived Intangible Assets [Line Items]
Net non-utility plant	853
Intangible assets	1,090
Long-term debt	1,032
PG&E Project | Secured Related to Project Debt
Finite-Lived Intangible Assets [Line Items]
Net non-utility plant	$ 288
Con Edison Development | PG&E Project
Finite-Lived Intangible Assets [Line Items]
Aggregate power to be sold (in MW) | MW	680