Summary of Significant Accounting Policies and Other Matters - Long-Lived and Intangible Assets (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) MW	Mar. 31, 2020 USD ($)
Finite-Lived Intangible Assets [Line Items]
Net non-utility plant	$ 43,889	$ 44,435
Intangible assets	1,557	1,532
PG&E Project
Finite-Lived Intangible Assets [Line Items]
Net non-utility plant	819	802
Intangible assets	1,057	1,039
Long-term debt	1,001	980
PG&E Project | Secured Related to Project Debt
Finite-Lived Intangible Assets [Line Items]
Net non-utility plant	$ 282	$ 274
Con Edison Development | PG&E Project
Finite-Lived Intangible Assets [Line Items]
Aggregate power to be sold (in MW) | MW	680