Summary of Significant Accounting Policies and Other Matters - Long-Lived and Intangible Assets (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) MW	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Finite-Lived Intangible Assets [Line Items]
Accumulated amortization	$ 126,000,000	$ 29,000,000
Amortization of intangible assets	99,000,000	14,000,000	$ 9,000,000
Amortization expense, 2020	100,000,000
Amortization expense, 2021	105,000,000
Amortization expense, 2022	105,000,000
Amortization expense, 2023	105,000,000
Amortization expense, 2024	105,000,000
Asset impairment	2,000,000
Impairment charges on long-lived assets		0	0
Impairment charges on intangible assets		0	$ 0
Net non-utility plant	43,889,000,000	41,749,000,000
Intangible assets	1,557,000,000	1,654,000,000
Long-term debt	19,973,000,000	18,145,000,000
PG&E Project
Finite-Lived Intangible Assets [Line Items]
Net non-utility plant	819,000,000	885,000,000
Intangible assets	1,057,000,000	1,125,000,000
Long-term debt	$ 1,001,000,000	1,050,000,000
PG&E Project | Con Edison Development
Finite-Lived Intangible Assets [Line Items]
Aggregate power to be sold (in MW) | MW	680
PG&E Project | Secured Related to Project Debt
Finite-Lived Intangible Assets [Line Items]
Net non-utility plant	$ 282,000,000	292,000,000
Other Intangible Assets
Finite-Lived Intangible Assets [Line Items]
Intangible assets, net	3,000,000
Accumulated amortization		7,000,000
Power Purchase Agreements
Finite-Lived Intangible Assets [Line Items]
Intangible assets, net	1,554,000,000	1,651,000,000
Accumulated amortization	$ 119,000,000	$ 22,000,000