Summary of Significant Accounting Policies and Other Matters - Long-Lived and Intangible Assets (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 MW	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Finite-Lived Intangible Assets [Line Items]
Net non-utility plant		$ 45,564	$ 43,889
Intangible assets		$ 1,485	$ 1,557
Con Edison Development | PG&E Project
Finite-Lived Intangible Assets [Line Items]
Aggregate power to be sold (in MW) | MW	680