Summary of Significant Accounting Policies and Other Matters - Long-Lived and Intangible Assets (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($) MW	Dec. 31, 2018 USD ($)
Finite-Lived Intangible Assets [Line Items]
Net non-utility plant	$ 42,152	$ 41,749
Intangible assets	$ 1,630	1,654
PG&E Project
Finite-Lived Intangible Assets [Line Items]
Net non-utility plant		859
Intangible assets		1,108
Long-term debt		1,041
PG&E Project | Secured Related to Project Debt
Finite-Lived Intangible Assets [Line Items]
Net non-utility plant		$ 289
Con Edison Development | PG&E Project
Finite-Lived Intangible Assets [Line Items]
Aggregate power to be sold (in MW) | MW	680